机体对刺激产生的反应必须有完整的反射弧存在，反射弧由感受器——神经中枢——效应器组成。
参考答案：对
—Jim jumped much _______ than John.
—Yes. He got the first in the sports meet. [ ]
A. high
B. higher
C. highest
D. the highest
机修与化验室经常接触哪些危险化学品？
