Question

which two are most closely related?
crocodile and tortoise
iguana and alligator
tortoise and alligator
alligator and crocodile

Explanation:

In biological classification, the closer the shared taxonomic rank (like order, family), the closer the relationship. American Alligator (Alligator mississippiensis) and Nile Crocodile (Crocodylus niloticus) share the same order (Crocodylia). Other pairs (e.g., Iguana - Alligator have different orders; Tortoise - Alligator have different orders) have more distant taxonomic separations.

Answer:

Alligator and Crocodile