1) 有些动词用一般现在时代替完成时：
hear, tell, learn, write , understand, forget, know, find , say, remember.
I hear (= have heard) he will go to London.
I forget (=have forgotten) how old he is.
2) 句型 " It is … since…"代替"It has been … since …"
3) It is (= has been) five years since we last met.
