以下真皮适用于皮革服装材料的是（）。
A.羊皮
B.牛皮
C.猪皮
D.马皮
参考答案：A
It’s said that the early European playing-cards ______ for education.
A．have designed
B．were designed
C．have been designed
D．were being designed
右下45缺失，右下6近中倾斜20°，右下3稳固（）
A.半固定桥
B.种植固定桥
C.复合固定桥
D.单端固定桥
E.双端固定桥
