I have waited for May _____ half an hour _____ but she has not appeared _____

I have waited for May for half an hour already,but she has not appeared yet.
这句话是现在完成式
而现在完成式有几个关键字
already - 用於肯定句
yet - 用於问句及否定句(否定句一般是在句子后面)
ever - 用於问句
never - 用於否定句（句子中间）
上面这一句句子前面是肯定句,所以用already.
后面一句是否定句,所以用yet.
时间是用at for
而这里是我等了一个半小时所以是用for
因为不是说几点!
希望可以解答你的问题!
不会可以在线交谈!