—_______ music lessons do you have every week?
—Two. [ ]
A. How much
B. How
C. How many
答案:C
可发生急性心脏压塞征的心包腔内积血量是()
A.50ml
B.100~200ml
C.250ml
D.300ml
E.350ml
引起电动机本体温度及电动机轴承温度升高都有哪些原因?