The sentence Dogs and cats sometimes fight in a veterinarian's waiting room is A) a simple sentence. A simple sentence has only one independent clause, and this sentence has only one independent clause (only one verb) so it has to be simple.
The given sentence above is an example of a simple sentence. It is a simple sentence because it only consists of one independent clause with a subject/s and verb/s. It contains a compound subject which is "dogs and cats" and a single predicate which is "fight".
