The term abiotic means something that is not living; it is devoid of life. Abiotic materials are still part of an ecosystem, but they are not living organisms. Of the answer choices, only one is a nonliving thing, a rock. The other options are all living organisms and are biological rather than physical.

NASA provides some background on the Sun compared to other stars, "Of course, the star that appears the brightest to all of us on Earth is the Sun. Although it is a rather typical star, not all that different from many of the ones you see at night, we live so close to it that it outshines everything else. Even the next closest star is more than a quarter of a million times farther from Earth, so it is not surprising that the light from the Sun overwhelms that from other stars." Due to the Earth's close (in relative terms) proximity to the Sun, it appears brightest to use because it is closer than all other stars in the galaxy.

The stage in the water cycle where water is heated by the Sun and turns to vapor is evaporation. The water absorbs heat from the Sun's rays and slowly releases it into the atmosphere. Water changes from a liquid state to a gaseous state (vapor) and returns to the atmosphere. The oceans of Earth are the largest collection of water so therefore the most evaporation and precipitation take place over the ocean. Water moves out of the oceans during the process of evaporation.

Gravity on earth pulls objects downward toward the ground. Rain is a good example: the clouds don't "throw" the rain to the ground, but instead, when there is so much water that it gets heavy for the cloud to hold, the water then falls to the ground because of gravity. In this example, the roots will grow downwards because of gravity. Geotropism is the influence of gravity on plant growth or movement. "Geo" means earth or ground, and "tropism" means a plant movement triggered by a stimulus. In this case, the stimulus is gravity. Roots explore the soil looking for water and nutrients to absorb.

The fact that it is hard work to run or walk uphill but much easier to run downhill shows how gravity pulls things downward. If you are going downhill, gravity is working with you to help you get there, but if you're going uphill you have to work against gravity. Note that the heights of trees isn't really constrained by gravity but instead by the kind of tree, the nutrients it receives, and those things. The fact that big planes can fly also isn't good evidence for gravity; planes use advanced technology to counteract the force of gravity, or otherwise they'd be pulled down. And although the stars in the sky are affected by gravity in their own way, they're not good examples of how things are pulled downward by gravity since to us from our vantage point they're way up in the sky.

NASA provides some background on the Sun compared to other stars, "Of course, the star that appears the brightest to all of us on Earth is the Sun. Although it is a rather typical star, not all that different from many of the ones you see at night, we live so close to it that it outshines everything else. Even the next closest star is more than a quarter of a million times farther from Earth, so it is not surprising that the light from the Sun overwhelms that from other stars." Due to the Earth's close (in relative terms) proximity to the Sun, it appears brightest to use because it is closer than all other stars in the galaxy.

Gretel's claim is supported by the research from NASA that her teacher presented. The Sun appears to be the brightest star because it is closest to Earth. It does not appear brightest because its the hottest, largest, or the brightest in the galaxy. "We live so close to it that it outshines everything else." This is the reason the Sun looks so bright.

The Lithosphere- contains all of the solid land of the planet's crust, the semi-solid land underneath the crust, and even the molten part of Earth’s core.

The Hydrosphere- contains all the water of the planet, which exists in solid, liquid, and gas forms. Water flows as precipitation from the atmosphere down to Earth's surface, as rivers and streams along Earth's surface, and as groundwater beneath Earth's surface. Most of Earth's freshwater, however, is frozen.

The Biosphere - contains all the planet's living things. This sphere includes all of the microorganisms, plants, and animals of Earth. Within the biosphere, living things form ecological communities based on the physical surroundings of an area. These communities are referred to as biomes. Deserts, grasslands, and tropical rainforests are three of the many types of biomes that exist within the biosphere.

The Atmosphere-contains all the air in Earth's system. The upper portion of the atmosphere protects the organisms of the biosphere from the sun's ultraviolet radiation. It also absorbs and emits heat. This sphere is also where weather occurs.

Most Earth events involve interaction between multiple spheres. For example, rain is the movement of water (the hydrosphere) from the atmosphere to the lithosphere where it collects in lakes, rivers, or streams. Water is an important resource for inhabitants of the biosphere.

The stage in the water cycle that returns water to Earth is precipitation. Depending on the weather conditions, the temperature on the Earth's surface and in the atmosphere, and the topography of the land will determine the amount and type of precipitation. Precipitation forms when the droplets in the clouds are too heavy and fall back to Earth. Rain will fall when both the atmosphere and surface temperatures are above freezing. Hail will form when there is a thunderstorm, the temperature in the atmosphere is below freezing, and the surface temperature is above freezing. Snow forms when the temperature is below freezing in the atmosphere and on the surface of Earth. Finally, sleet is formed when the temperature in the atmosphere is above freezing, and the surface temperature is below freezing.

The passage informs readers that the ocean only contains about three to four percent salt, so there is not an equal amount of water and salt in the oceans. The text also mentions that 97% of Earth's water is saltwater, so the majority of water is not found in clouds. Water evaporates from the ocean, not salt, and this is explained in the passage by describing how the oceans become saltier as water evaporates. This leaves rivers contain salt as the correct statement. Rivers have tiny amounts of salt in their water that is dumped into oceans.