I like the colour of the jeans. So I'd like             . [ ]

A. buying one

B. to buy one

C. buying a pair

D. to buy a pair

在FeSO₄和CuSO₄的混合溶液中加入一定量锌粉，充分反应后过滤，向滤渣中加入少量稀硫酸，有气泡产生。则滤液中一定不含有的溶质是      。