Read the sentence from “Stress for Success.” That is what causes [children with anxiety disorders] to make mountains out of molehills.

What is the meaning of the figurative phrase “to make mountains out of molehills”?

A. to seek help for a serious health issue instead of waiting
B. to collect many objects to add to a huge selection
C. to make a less significant problem into one of greater importance
D. to make a plan far in advance instead of waiting until the last minute