离心式水泵主要动力源是（）。
A.水泵
B.闸阀
C.管路
D.电机
参考答案：D
郁金组织中有
A．动物体的某一部分B．动物体某些部分的加工品C．动物的排泄物D．动物除去内脏的干燥体E．动物的干燥全体
— Hi, David! How was your trip to Beijing?
— Wonderful! I had never had ________ holiday in my life.[ ]
A. a most exciting
B. a more exciting
C. the most excited
D. the more excited
