Why Did Louis and Mary Leakey Choose Olduvai Gorge as the Place

Why did Louis and Mary Leakey choose Olduvai Gorge as the place to spend decades doing their research?

A) No one had worked there before, so anything they found would make them and their work famous.
B) Several skeletons of early hominins had been found there already, so they knew it was a good place to work.
C) The layers exposed by the gorge were known to include ancient stone tools and animal remains.
D) The environment around Olduvai is very wet and forested, and the Leakeys knew that early primates had evolved in a well-watered habitat.