不锈钢按用途分为（）。
A.耐酸碱腐蚀
D.耐高温腐蚀
C.奥氏体型
D.耐大气腐蚀
参考答案：A, B, D
Walking exercises ____ be boring at times, but on a clear sunny morning nothing could be better. [ ]
A. may
B. will
C. must
D. should
