舷外二冲程油除具备普通二冲程的性能，还必须具备生物毒性小，防水性和防锈性好等性能。
参考答案：对
We woke in the morning early than we _____ because the clock in the room was one hour ahead![ ]
A. had expected
B. were expecting
C. would expect
D. would be expected
1952年12月，在英国伦敦发生了骇人听闻的“伦敦烟雾事件”。在短短的4天内，4000余人丧生。造成这一惨案的原因是
A．土壤污染
B．水污染
C．大气污染
D．工厂噪声污染
