剪切应力在疲劳裂纹()起重要作用。
A.第一阶段扩展
B.第二阶段的扩展
C.裂纹源的形成
D.脆断
参考答案:A
—Some Chinese students find it hard to get used to the life in London.
—Exactly, ______ they’ve learnt a lot about the city before.
A.if
B.now that
C.as though
D.even though
可与硝酸银试剂产生银的黑色沉淀的药物是()
A.维生素B1
B.维生素B2
C.维生素B6
D.维生素B12
E.维生素C