二次脱硅是在（）中加入石灰乳。
A、脱硅机
B、过滤机
C、沉降槽
D、缓冲槽
参考答案：D
.I want to buy a rope which is _____________this one.
A．twice as longer as
B．as twice long as
C．twice the length of
D．as twice as
碳纤维不饱和聚酯树脂复合材料疲劳极限可达其拉伸强度的( )。
A．70%～80% B．50%～60% C．40%～50% D．30%～40%
