Here is the original item:
As Alex navigated the narrow row of chairs. (A) His heavy book bag bumped the large soda perched on Teresa's desk, (B) sending a shower of diet cola into the girl's lap, (C) soaking her jeans.
You wanted to do this:
As Alex navigated the narrow row of chairs. His heavy book bag bumped the large soda perched on Teresa's desk. Sending a shower of diet cola into the girl's lap, soaking her jeans.

A period after desk makes a fragment. Sending a shower of diet cola ... is a participle phrase, which cannot stand alone as a complete sentence.

You might want to review the rules.

Go back to the item to try again.