正常工作时，操作站上的启动/旁通钥匙开关应置（）位置上
A、关断
B、旁通
C、正常
D、启动
参考答案：D
Jack wasn’t saying anything, but the teacher smiled at him _______he had done something very clever.
A．as if
B．now that
C．while
D．though
按钮应接在下列（）端点上。
A、X000
B、Y000
C、M0
