have an internal clock that controls the beating of our heart, and the of our breathing.
A. Human being; steps
B. Humans; pace
C. Human beings; steps
D. Man; pace
网友回答
A. Human being; steps
(答案→)B. Humans; pace
C. Human beings; steps
D. Man; pace
解析：B 考察名词。句义：人类体内有一个生物钟，它控制我们的心跳和呼吸的节奏。因为谓语是have，所以排除AD，humans=human beings，但steo的含义是脚步，步伐；