细菌内毒素的成分是（）
A.H抗原
B.肽聚糖
C.O抗原
D.脂多糖
E.荚膜多糖
参考答案：D
We meant to finish the work by dark, but we were so tired that we could not ______.
A．hold on
B．last on
C．carry on
D．keep to
发生火灾时，（）信号具有最大优先权。
A、背景音乐
B、寻呼找人广播
C、消防广播信号
D、以上都对
