量热仪外筒的水（）更换一次，并应在水中放（）克食用盐，以增强水的导电性能。
参考答案：每半年，1-2
-I'm afraid I can't return your book by Friday.
-________. There is no need to return it hurriedly. [ ]
A. Go ahead
B. Take it easy
C. Come on
D. Take your time
调校合格后的安全阀必须铅封。（）
