甲烷是天然气中含量最多的成分，它是无色，比空气重的可燃气体。
参考答案：错
The soldiers tried their best and did what they could _______ against the flood.
A．fight
B．to fight
C．fighting
D．fought
下列属于特异性感染的是
A．急性胰腺炎
B．脓毒症
C．气性坏疽
D．丹毒
E．痈
