Final answer:
The giraffe is the only animal with four true knees.
Step-by-step explanation:
The correct answer is b) Giraffe.
Giraffes are the only animal with four true knees in the list provided. The front legs of a giraffe bend at the knee joint in order to lower the head to drink water or reach the ground.
Other animals listed, such as elephants, horses, and rhinos, have elbows or wrists rather than knees, while the answer options of rabbit, mouse, sea cow, goat, zebra, deer, elk, hippopotamus, kangaroo, and monkey do not have four knees.