一般现在时代替过去时

1 )"书上说"，"报纸上说"等。
The newspaper says that it's going to be cold tomorrow.
报纸上说明天会很冷的。
2) 叙述往事，使其生动。
Napoleon's army now advances and the great battle begins.

一般现在时代替完成时

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.

一般现在时代替进行时

1) 句型：Here comes… ； There goes…
Look, here comes Mr. Li.