Since a group of lions is called a "pride," we are looking for an answer choice in which the first blank is an animal, and the second blank describes the species-specific name for a group of those animals. Thus, the best answer choice is "birds are to flock," because a group of birds is referred to as a "flock."

Since a caterpillar eventually becomes a butterfly, we need to pick out another pair of words in which the first word describes an animal that eventually metamorphoses into a form that the second word describes. While "flower is to leaf" might look like an answer, flowers don't become leaves—both are parts of a plant. Similarly, "insect is to dragonfly" is not correct either since an insect does not become a dragonfly—a dragonfly is a kind of insect. "Tadpole is to frog" is the correct answer because just like a caterpillar metamorphoses into a butterfly, a tadpole metamorphoses into a frog.

"Troop" is a noun that can mean "a group of soldiers, especially a cavalry unit commanded by a captain, or an airborne unit," so a troop is made up of soldiers, and we need to pick out an answer choice that describes what kind of thing a flock is made up of. While "bird," "horse," and "firefly" may each look like a potentially correct answer because each one is a living thing, "bird" is the correct answer because just like a troop consists of a number of soldiers, a flock consists of a number of birds.

Fish are covered in scales, so we need to pick out an answer choice that is a noun describing what porcupines are covered in. While "quills," "ooze," and "feathers" may each look like a potentially correct answer, porcupines are covered in quills, so "quills" is the correct answer.

Alligators live in swamps, so we need to pick out an answer choice in which the first word is a location, and the second word an animal that would be likely to live in that location. All of the potential answer choices fit this format, but sharks do not live in deserts, pigs don’t live in oceans, dolphins don’t live in the mountains, and gorillas don’t live on prairies, so none of those answers can be correct. Black bears do live in forests, however, just as alligators live in swamps, so “forest is to black bear” is the correct answer.

Since birds fly, we need to pick out an answer choice that describes what fish do. Of the listed answer choices, two are verbs - "crawl" and "swim." Since fish swim, "swim" is the correct answer choice.

Since cats make sound by meowing, we need to pick a word that describes the sounds dogs make. Since dogs make sound by barking, "bark" is the correct answer.

Since birds live in nests, we need to pick out a word that describes what kind of animal lives in a den. Since "den" means "the lair of a wild usually predatory animal," "bear" is the correct answer, since "bear" is the only answer that is a predatory wild animal of the possible answer choices, and bears specifically hibernate in dens.

A young bear is called a "cub." So, to solve the analogy, you need to pick out the answer choice in which the first word is an animal and the second word is the name given to a young animal of that type. A young cow is called a "calf," so "cow is to calf" is the correct answer. (A "gander" is a name given to a male goose, and a "buck" is a male deer, while a "doe" is a female deer.)

"Puppy and dog" discuss the juvenile and grown stages of a living thing, with the younger discription first and the older one second. The only choice that matches this is "child is to adult."