在△ABC中，∠A=3∠B，∠A﹣∠C=30 °，则∠A=（ ）度，∠C=（ ）度
90°，60°
I don't think he could have done such a stupid thing last night, ______? [ ]
A. do I
B. could I
C. did he
D. has he
钢材表面氧化皮因锈蚀而全面剥落且已普遍发生点蚀，其锈蚀等级为（）
A.A级
B.B级
C.C级
D.D级
