Of the Following Organisms, the Best Index Fossils Would Be

Of the following organisms, the best index fossils would be:

A) bacteria, because they have existed in widespread geographic areas since life first began.
B) a specific type of trilobite that existed for only a short geologic time in widespread geographic areas.
C) cockroaches, because they have existed in widespread geographic areas almost since the first appearance of insects.
D) a specific type of bryzoa that existed for only a short geologic time in very limited geographic areas.