问题补充：
My mother often some money some useless things.
A. spends ; buying
B. spends ;to buy
C. pays ; buying
D. pays ; on
答案：
(答案→)A. spends ; buying
B. spends ;to buy
C. pays ; buying
D. pays ; on
解析：此题重点考查cost，spend，pay，take四个花费的区别；cost的主语是物常用句型结构是sth cost some money；spend的主语是人，常用的句型结构是sb spend some time/money in doing sth; pay的主语是人，常用句型结构是sb pay something some money；take的主语是it，常用句型结构是it takes sb some time to do sth,综上所述，根据句意选择A.
