18×23=12（吨）．
即18吨的23是 12吨．
故答案为：12．
My mum was born ______ May 2nd, 1971. [ ]
A. in
B. on
C. at
D. from
焊接黄铜时，为了防止锌的蒸发，焊丝中含有（）元素。
A.Sn
B.AI
C.Si
D.Mn
