It is in their ability to speak humans from animals.A. which; differB. that; differentC.

问题补充：

It is in their ability to speak humans from animals.

A. which; differ

B. that; different

C. that;differ

D. which;different

答案：

A. which; differ

B. that; different

(答案→)C. that;differ

D. which;different

解析：

第一空考查的是强调句，第二空考查动词differ from“于…不同”，句意是：人类和动物的不同在于他们说话的能力。选C。