井下CO的来源是（）。
A、采煤机割煤
B、掘进机作业
C、有机物的腐烂
D、井下火灾和瓦斯与煤尘爆炸及爆破
参考答案：D
He wrote his novel when he was .
A．five, fifties
B．fifth, fifty
C．fifth, fifteen
D．five, fifty
字符型变量以char类型表示，它在内存中占________位bit。
