Answer:
a. Before the game even started. I could tell team morale was low.
Step-by-step explanation:
We are looking for a sentence fragment, or an incomplete sentence. Out of the answer choices, only choice a has a dependent fragment.
a. Before the game even started. I could tell team morale was low.
The first part, "Before the game even started," is not a sentence but rather a clause. It has a subject and verb, to be sure, but it is not a complete thought.
Choices b and c are both complete sentences that use correct clauses.