1) 有些動詞用一般現在時代替完成時：
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.