食管的第二狭窄在（）
A．起始处
B．穿膈处
C．与左主支气管交叉处
D．与右主支气管交叉处
E．与胃相接处
参考答案：C
Jim ______ get up very late. But now he ______ getting up early. [ ]
A. used to; is used to
B. used to; used to
C. was used to; is used to
D. was used to; used to
电源的-5V输出，主要是为（）提供电力。
A.ISA总线插卡
B.PCI总线插卡
C.AGP插卡
D.USB设备
