Why using two manipuled variables in an expierement would be wise

Which sentence best expresses the differing opinions of these two book reviews?

The wings of insects, birds, and bats evolved independently but carry out similar functions. this is an example of a. analogous structures. b. embryonic structures. c. vestigial structures. d. homologous structures.

Which of the following happened during the precambrian era? the first prokaryotic cells the first eukaryotic cells development of photosynthesis all of the above