Which of the following sentences is a complex sentence?

A complex sentence contains an independent clause and at least one dependent clause. In choice A, 'When Jung-hoon found a seat on the bus' is the dependent clause, and 'he hoped he would have a quiet ride' is the independent clause, making it a complex sentence. Choices B, C, and D do not contain this structure; therefore, they are not complex sentences. Choice B is a compound sentence with two independent clauses joined by a coordinating conjunction. Choice C is a simple sentence with only one independent clause. Choice D is also a simple sentence with only one independent clause.