选：A
分析：
见牛津高阶英汉双解词典,第二个意项
spend sth (on sth/ in doing sth):use (time,etc) for a purpose,花（时间等）在某事上/做某事
这里还可以说,She spends two hours on piano every day.
或者,She spends two hours in practising the piano every day.
in可以去掉；至于为什么 practising,是把动词 practise 变成了名词性质的动名词practising .