Answer:
The sentence is C. complex.
Step-by-step explanation:
A complex sentence is the result of joining together an independent clause and a dependent or subordinate clause.
An independent clause is able to express a complete thought, making sense on its own. That is the case with the first clause in the sentence:
"The muscles in my wrist are cramping."
A dependent clause, on the other hand, is not able to express a complete thought on its own. It needs the main clause to give it context. A dependent clause begins with a subordinating conjunction - in this case, "as":
"As I struggle to type my essay."
Therefore, what we have in "The muscles in my wrist are cramping as I struggle to type my essay" is a complex sentence.