pay (for) and buy                                  
     典型错误：

     Typical mistake: *Come on, I'll pay you a drink.
   
You pay a person, you pay a bill, and you pay sums of money, but you pay for something you buy.
       You can have the room free, but you'll have to pay me £10 a week for your meals. (房间免费，但每周你要付十镑饭费。)

    When we want to talk about paying for a drink or a meal for a person, we usually use the verb buy (or get).
要替某人付酒钱或饭费，通常使用动词buy(或get).
       Come on, I'll buy you a drink. (走吧，我请你喝酒。)    Let me get you a drink. （我请你喝一杯）
       Can I buy you lunch?（我可以请您吃午饭吗）
    Pay for can also express the idea of paying money that somebody else owes.

   pay for可以表达还某人所欠的钱的意思。
       Don't worry about money; I'll pay for you.（不用担心钱；我会还你的。）