Main Idea Practice Test

Read the passage, then answer the question.

In the 1500s, European explorers began sailing farther across the oceans, searching for new trade routes and resources. Several forces pushed this change. Some nations wanted direct access to valuable goods like spices and silk, which were costly when bought through long chains of merchants. Others hoped to gain wealth and influence by claiming new territories. Improvements in ship design and navigation tools also made longer voyages more possible.

One major result was the Columbian Exchange, a transfer of plants, animals, and ideas between the Eastern and Western Hemispheres. Crops such as potatoes and corn traveled to Europe and became important foods in many countries. In the other direction, horses and certain farm animals arrived in the Americas, changing transportation and farming. New trade networks formed, and ports grew into busy centers of commerce.

These voyages also changed how societies understood the world. Maps became more detailed, and people learned about distant regions and cultures. At the same time, exploration encouraged competition among nations. Countries invested in fleets and colonies, hoping to control trade and increase power.

The passage emphasizes that ocean exploration was not just about adventure. It reshaped economies, diets, and global connections, creating lasting effects on how societies developed and interacted.

Which statement best captures the main idea of the passage?

Read the passage, then answer the question.

In 1928, a scientist named Alexander Fleming returned to his laboratory after a short vacation. He noticed something unusual in a stack of petri dishes where he had been growing bacteria. One dish had been accidentally contaminated by a mold, and around that mold the bacteria were not growing. Many people might have thrown the dish away, but Fleming paused to investigate. He realized the mold was releasing a substance that killed or stopped the bacteria. This simple observation became the starting point for penicillin, the first widely used antibiotic.

At the time, infections were a major danger. Even a small cut could become infected, and illnesses like pneumonia often led to death. Doctors could clean wounds and try to keep patients comfortable, but they had few reliable ways to stop harmful bacteria once an infection spread. Fleming’s discovery suggested a new approach: instead of only supporting the body, medicine could directly attack the cause of many infections.

However, the discovery did not change the world overnight. Fleming could not easily produce enough penicillin to treat large numbers of people. Years later, other researchers worked to purify the substance and find methods to make it in larger quantities. During World War II, the need for effective treatments pushed governments and laboratories to cooperate. Penicillin production increased, and the medicine reached soldiers and civilians who otherwise might have died from infected wounds or common diseases.

The effects of antibiotics were enormous. Surgeries became safer because doctors could prevent or treat infections afterward. People recovered from illnesses that once filled hospitals for weeks. Over time, antibiotics helped increase average life expectancy and changed how communities responded to disease outbreaks. Yet the passage also hints at a responsibility. Because bacteria can adapt, antibiotics must be used carefully so they remain effective.

Overall, the story of penicillin shows how a careful observation, followed by teamwork and persistence, can transform society’s ability to fight disease.

Which statement best captures the main idea of the passage?