离心泵的叶轮是对液体做功的部件。
参考答案：对
儿童服用可发生牙齿变色的药物是（）
A.盐酸土霉素
B.多西环素
C.盐酸美他环素
D.氯霉素
E.环孢素
A_____girl named Dong Xinyi looked after her disabled father.[ ]
A. three-year-old
B. three-years-old
C. three years old
