Answer: The correct answers for the fill in the blanks are-
1) B) Homologous structures.
2)C). Cats and humans share a common ancestor.
Homologous structures/organs are those parts of two organisms that look similar in their form/structure because they share common ancestor (that is they have evolved from a common ancestor) but due to different adaptation, perform different function.
Example -The legs of a human and the limbs of a cat, which have evolved from a common ancestor.