小军买了m支圆珠笔，每支n元，找回4元，小军原来付给售货员______元钱．
依题意有：小军原来付给售货员（mn+4）元钱．
故答案为：（mn+4）．
It was in the factory _____ I worked when I was twenty _____ I met Linda who later became my wife. [ ]
A. that; where
B. where; that
C. that; that
D. where; where
鉴别硬水和软水的方法是______；生活中降低水的硬度的方法是______．
