现在完成时的句式转化：
I have finished all my homework.
否定句： I haven’t finished all my homework.
一般疑问句： Have you finished your homework? Yes, I have. No, I haven’t
现在完成时中的常用副词：already, yet, ever, never, just,
I have already finished my homework.
I haven’t finished my homework yet.(还）
Have you finished your homework yet?(已经）
Have you ever visited China?No, I have never visited China.
I have just finished my homework.
