Since a star is a single unit that, when combined with other stars, forms a constellation, we need to find a single unit that, when combined with others, creates a whole class. Since many students make up a class, the correct answer would be "student." At first glance, the answer may appear to be teacher, as every class is led by a teacher, but a class is made up by a body of students and has only one or two teachers. In addition, a teacher is the head of the class but is not part of the class itself.

Since a mug is typically made of ceramic material, we need to find an object that is typically made of glass material. Windows are primarily made of glass, therefore the correct answer is "window."

Sweaters are often made of wool. Therefore, we must look for the answer that shows a relationship between a product and the material from which it is made. Shoes are often made of leather, so the correct answer is "shoe is to leather."

"Tornado" is a noun that means "a mobile, destructive vortex of violently rotating winds having the appearance of a funnel-shaped cloud and advancing beneath a large storm system." So, because a tornado is a natural disaster that consists of wind, we need to pick out an answer choice in which the second word represents a natural disaster caused by or composed of the first word. "Rain is to rainbow" might look like a potentially correct answer, but since a "rainbow" is not a natural disaster, it cannot be the correct answer. However, because a snowstorm is a natural disaster created by snow, just like a tornado is a natural disaster created by wind, "snow is to snowstorm" is the correct answer.

A "galaxy" is the name given to a collection of "stars." Our galaxy is called "the Milky Way." To solve this analogy you need to determine which of these is a name given to a collection of "books." The correct answer is a "library."

A skeleton is comprised of bones, so we need to pick out an answer choice in which the first word is made up of the thing the second word refers to. While "thread is to cloth" might look like a good answer choice because cloth is made up of thread, it can't be the correct answer because the two words are in the incorrect order—skeletons are made of bones, but thread is not made of cloth. Log cabins are made up of logs, however, so "log cabin is to logs" is the correct answer.

Since a snowflake is a single unit of snow, and a snowdrift is composed of a lot of snowflakes, we need to pick out a word that describes something that is composed of a lot of water drops. Since "downpour" is the only answer choice that is made up of lots of raindrops, "downpour" is the correct answer.

An "omelet" is made using "eggs." So, which of these is something that is made using "flour?" The correct answer is a "cake."

Since hay is the material that comprises a haystack, we must find that material that comprises an igloo. Since igloos are made of ice, the correct answer is "ice."

"Jam" is usually made from "fruit," so to solve this analogy you need to figure out which of these answer choices "cheese" is usually made from. The correct answer is that "milk" is used to make "cheese."