真空系统不允许有丝毫泄漏。
参考答案：错
解析：真空系统有轻微泄漏时，可以增开真空泵来提高真空度。
Some “healthy” habits, such as shower every day and sitting on the loo, _____ be bad for you.
A．can
B．should
C．must
D．shall
吐蕃最强盛的时候曾攻下河西走廊，攻入过长安，打入过南诏国。
