一般来说，就是熟人见面打个招呼，相当于hi，hello。不过随着时代的发展，现在越来越少这么说了。现在熟人见面打招呼一般用得比较多的有：hi，嗨，你好，您好，最近还好吧，去哪里？干什么去？

It depends on in what scenarios it happened.

To me, in most cases, it refers to B, but it becomes less and less popular in China nowadays. Now we greet with 'how are you?'(怎么样?) or just smile directly.

In some scenarios it could be A especially before meal time.

C only makes sense to me if I'm asking someone or asked by someone in very particular scenario like at home or overtime working after meal time.