3.Someonedidhandinabag,whichis_______.
A.ablacknylonoxfordbag
B.abrownleatherbag
C.ablackcomputerbag
D. o
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4. Which of the following is the man’s mobile phone number?
A. 65940117387.
B. 65940113778.
C. 65940113787.
D. o
PCVD法是一种管外制造光纤预制棒的化学气相沉积技术。
A. 对
B. 错
设f'(a)=0,f"(a)>0，则【】
A. f′(a)是f′(x)的极大值
B. f(a)是f(x)的极大值
C. f(a)是f(x)的极小值
D. (a,f(a))是曲线y=f(x)的拐点
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