Ostrich is to rattlesnake as iguana is to ________.?

This really is a bizarre question and you could probably justify any of these answers. I would say alligator, but honestly that's just the relationship that jumps out at me. Ostriches, alligators, rattlesnakes and iguanas are all diapsids, a group of animals that also includes the dinosaurs. Crocodilians (including alligators) and birds are on one branch of the family tree, and snakes and lizards are on the other branch. So, the ostrich and the rattlesnake have (roughly) the same evolutionary relationship as the iguana and the alligator.