There is an important difference between humans and chimpanzees. Chimpanzees walk

A. There is an important difference between humans and chimpanzees that walk on four legs. 

B. Chimpanzees walk on four legs, so they are importantly different from humans. 

C. An important difference between humans and chimpanzees is that chimpanzees walk on four legs. 

D. There are important differences between humans and chimpanzees one of which is that chimpanzees walk on four legs.