How Did Life on Earth Get to Be So Diverse

How did life on Earth get to be so diverse?

A) There were lots of different living things ever since life began.
B) Conditions on Earth are always changing and so species adapt to survive and this change leads to the development of new species from the old ones.
C) New species tend to appear randomly whenever new environmental conditions arise.
D) Life actually isn't all that diverse because species keep going extinct as conditions on Earth change.
E) Conditions on Earth are constant enough that new species have time to develop.