Please help a.s.a.p. (answer has to be 100% correct btw)

2. Which of the sentences contain both an independent and a dependent clause?
A. He was listening intently to the radio, and he didn't hear the doorbell.
B. As she entered the auditorium, she tripped over a backpack that had been carelessly left in the doorway.
C. Visiting the aquarium turned out to be quite an adventure; I enjoyed it thoroughly.
D. We understand the environmental concerns of the farming community, but we are aware that business owners have another point of view.