What is the probable sequence in which the following clades of animals originated, from earliest to most recent?
1. tetrapods
2. vertebrates
3. deuterostomes
4. amniotes
5. bilaterians
a. 5→3→2→4→1
b. 5→3→2→1→4
c. 3- 5--4-2 1
d. 3→5→2→1→4