Answer:
Complex sentence.
Step-by-step explanation:
A complex sentence is a sentence that contains at least one independent clause and one dependent clause. It can also contain one or more dependent clauses but only one independent clause.
In the given sentence, the independent clause is "he will sometimes read comics" while the dependent clause is "although Caleb enjoys reading". The independent clause can stand on its own as a full sentence while the dependent clause just provides extra information/ detail to the already complete sentence.
Thus, the correct answer is a complex sentence.