Answer:
The sentence "Presidential conventions occur every four years during the summer" is a simple sentence.
Step-by-step explanation:
A simple sentence is formed by an independent clause. An independent clause has a subject and a verb, and is able to express a complete thought on its own. The sentence we are analyzing here is a simple sentence. It consists of only one clause, and that clause is independent. It makes sense on its own, not needing another clause to add information or context.
NOTE: If this question allows for more than option to be selected, then we can also choose "complete sentence" as a correct option. A complete sentence has a subject and a finite verb, which is the case here.