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."

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."

A "gram" is a measure of "weight," just as a "meter" is a measure of "height."

Since "yesterday" means "the day before yesterday," it is referring to a day in the past. We need to pick out a word that temporally describes "today." Since "present" means "existing or occurring now," and "today" means "this present day," "present" is the correct answer, because just as yesterday is thought of as being in the past, today is thought of as being in the present.

"Dozen" is a noun that means a group of twelve, so you need to pick out an answer choice that is a word that means a group of two "Couple" is a noun that can mean a group of two, so "couple" is the correct answer.

Since a compass is a device that displays directions, we need to pick out an answer that represents what a watch displays or measures. While "month" may look like the correct answer because it is a unit of time, it is too specific to be the right answer, as watches measure units smaller than months. Since watches display the time like compasses display direction, the correct answer is "time."

There are one hundred years in a century, as you might infer from the word's use of the prefix "cent-," which means hundred; just think of how a "cent," or a penny, is one-onehundredth of a dollar. So, to solve this analogy, you need to pick out an answer choice that describes how many years there are in a decade. There are ten years in a decade, which you might infer from the word's use of the prefix "dec-," which means ten and appears in other words like "decagon" (a ten-sided shape).

A triangle is a shape that has three sides, so we need to pick out an answer choice in which the first word is a shape and the second word is a number conveying the number of sides that shape has. While all of the potential answer choices except for “metal is to iron” fall into this pattern, only “square is to four” correctly matches the number of sides to the shape indicated. Because a square has four sides just like a triangle has three sides, “square is to four” is the correct answer.

You can measure weight in pounds, so to solve the analogy, you need to pick out an answer choice that describes a unit of measurement that you can use to measure an amount of liquid. Both "meters" and "yards" measure length or distance, and "height" and "size" aren't units of measurement at all. You can measure an amount of liquid in "gallons," so "gallon" is the correct answer.