锅炉（）适用长期停炉（一般超过1个月以上）。
A.压力保养
B.干法保养
C.湿法保养
参考答案：B
Many parents happily pay a lot of money, only ______ the tours are not rewarding enough for their children.
A．to find
B．find
C．having found
D．to have found
我国国家标准中规定亚硝酸钠的最大使用量为（）
A.0.05mg/kg
B.0.10mg/kg
C.0.15mg/kg
D.0.20mg/kg
E.0.50mg/kg
