选择题：Once environmental damage _________, it takes many

题目内容：

Once environmental damage _________, it takes many years for the system to recover. （分数：1 分）
A. has done
B. is to do
C. does
D. is done

参考答案：

She didnt _______ me for returning the wallet that

She didnt _______ me for returning the wallet that I found. （分数：1 分） A. so much

Are there any _____on the farm?（分数：1 分） A. horse B. chick C. chicken D. duck

Before ________ the road, please look both sides.（分数：1 分） A. crossing B. crossed

单元刚度矩阵表示的是那两组量之间的关系？ A.杆端位移与结点位移B.杆端力与结点位移C.结点荷载与结点位移D.杆端力与杆端位移