锅炉长时间停炉应关闭供水阀、进油阀、回油阀和回油网。所谓长时间停炉是指停炉（）以上。
A.1小时
B.5小时
C.12小时
D.24小时
参考答案：B
用单词的适当形式填空。
1. ______ (not be) late for school.
2. Let's ______ (practice) ______ (speak) French.
3. Mike ______ (have) ______ (do) his homework every day.
4. "No ______ (talk)" in the library. Can you see it?
5. What ______ the children ______ (do) in the park now?
投资组合能( )。
A．分散所有风险
B．分散系统性风险
C．分散非系统性风险
D．分散市场性风险
