Most biologists agree that evolution takes place extremely slowly, wit

Most biologists agree that evolution takes place extremely slowly, with species requiring millions and millions of years to accumulate enough small changes to gradually transform into new ones. For the first 4 billion years of Earth’s history, the only species known were bacteria, plankton, and algae. But the fossil record indicates that during a brief 30 million year span known as the Cambrian explosion, the eventual lineages of all major animal groups alive today appeared.

Which of the following, if true, provides at least a partial explanation for the discrepancy outlined above?

A. The fossil record only represents a small portion of the species alive at any given time.
B. The fossil record indicates a number of major extinction events in Earth’s history.
C. Some of the lineages found in the fossil record of the Cambrian explosion are no longer alive today.
D. Bacteria, plankton, and algae leave little evidence in the fossil record because of their physical structures.
E. The fossil record indicates a large diversity in the plant species inhabiting the Earth during the Cambrian explosion.

Source: McGraw-Hill's GMAT