耐火性能差的结构是（）。
A、钢筋混凝土结构
B、砖混结构
C、钢结构
D、素混凝土结构
参考答案：C
水泥的初凝和终凝
根据句意及所给提示，补全单词或用单词、固定短语、固定搭配的正确形式填空。
1. There are sixty m_______ in an hour.
2. He enjoy_______ ( help ) others in trouble.
3. Thanks for your_______ (invite) to the party.
4. It' s not right to _______ (浪费) time or money.
5. It's my _______ (责任) to take good care of my parents when they are old.
