Which of the following correctly describes the major types of animals?
a) all chordates share a common ancestor, but there is no common ancestor of all invertebrates.
b) all invertebrates are chordates; vertebrates are a group that is separate from both invertebrates and chordates.
c) all invertebrates are chordates; vertebrates are a group that is separate from both invertebrates and chordates.
d) chordates are the largest group, and it is subdivided into two groups: vertebrates and invertebrates.