Read the passage below.
did you know that crocodiles tend to have longer, pointed, v-shaped snouts while alligators generally have wider, rounder, u-shaped snouts? the signal word "while" serves what purpose?
a. it signals a similarity between alligators and crocodiles.
b. it signals a difference between alligators and crocodiles.
c. it signals that more information about crocodiles follows.
d. it signals that the reader is nearing the end of the text.

The correct option is B. It signals a difference between alligators and crocodiles.

Explanation:

Transitional words are words used to link phrases, sentences or even other words. That is to say, Transitional words' main purpose is to help the reader to progress through a certain text, from one idea to the next.

Such transitional words have been classified into several categories among which it is possible to name: Agreement, Addition, Similarity, Cause, Purpose, and Contrast, just to name a few.  

In the particular case of the transitional words to express contrast, they usually introduce a change the line of reasoning, including words such as in contrast, although, whereas and while, among many others.

Bearing the explained above, it could be said that in the passage shown, the word "while" serves to the purpose of signaling a difference or contrast between alligators and crocodiles.