Take a look at the sentence again:

Sima was so sleepy after her marathon studying session for calculus that she ordered a triple espresso before going to class once the caffeine kicked in, Sima knew that she wouldn't doze off on Dr. Ribley.

The problem occurs between class and once. Sima was so sleepy … begins a complete sentence. Once the caffeine kicked in, Sima knew … introduces the next complete sentence. Because these two parts have only blank space between them, they make a fused sentence, a major error.

To fix the problem, you could put a period after class and then capitalize the O for once.

Go to the next sentence.

HomeTermsExercises MOOCHandoutsPresentationsVideosRulesAboutShopFeedback