Answer: B. complex.
Step-by-step explanation:
A complex sentence is a sentence that consists of an independent clause and at least one dependent clause. An independent clause is a clause that can stand on its own (as opposed to a dependent clause).
Compound sentences, on the other hand, must contain at least two independent clauses. Simple sentence is a sentence which contains only one clause.
The sentence: 'If you are in line early, you’ll be sure to get the best tickets' is a complex sentence, as it contains a dependent clause 'If you are in line early' and an independent clause 'you’ll be sure to get the best tickets.'
There is also a subordinating conjunction 'if', which links a dependent clause to an independent clause.