简述钢材的机械性能。
参考答案：
强度极限、屈服极限、弹性极限、比例极限；常用作强度计算的是强度极限、屈服极限。
鱼是适应水中生活的一类动物，其呼吸器官是（ ）
A．肺
B．皮肤
C．气管
D．鳃
—Do you feel like________there or shall we take a bus?
—I'd like to walk, but since there isn't much time left, I'd rather we________a taxi. [ ]
A. to walk; take
B. walking; took
C. to walk; took
D. walking; take
