I don's know what to buy 为什么BUY前面要加TO?

I don's know what to buy 为什么BUY前面要加TO? i just don't know()myself A.what to buy for B.to buy what fo but I don't know what ____for them.A.buy B.buying C.to buy i want to buy a mobile but i don't know whether or what styl I don’t know what I should buy.(同义句)I don’t know _What to bu to,her,i,what,buy,for,don't,know连词成句 what are you going to buy前面加什么(问句)? I really don‘t know which one to buy If i want to buy LCD,what should i know? i don't know how to swim.i decided what to buy.这两个句子里面的how t what i have to buy? I didn’t know what (改为which )one to buy为什么这样改,wh