Answer:
The author's use of simile:
B. It helps the reader visualize the increased number of exoplanets discovered.
Step-by-step explanation:
A simile is a figure of speech used with the intention of making a comparison - stating a similarity - between two different things. A simile needs help of words such as "as" or "like".
In the text, the discovery of planets and exoplanets was compared to billiard balls in a pool game. First, discovering planets was similar to a regular game, in which it is easy to see and count the balls. But, as more and more exoplanets were discovered, scientists could no longer run tally. That is why it was like a pool player making a big, smashing break: planets, like the billiard balls, were everywhere. The text moves on the describe it as an "inordinate number". Therefore, we can say safely say the simile is being used to help the reader visualize the increased number of exoplanets discovered.