雙寫的原則是“重讀閉音節結尾，末尾只有一個輔音字母。第一是重讀音節，第二形式上是輔元輔，輔音+元音字母+輔音字母。如put,set,stop,swim都是單音節的例子；多音節的例子有begin,forget,admit,refer,equip等，都是重讀第二音節，而且形式上是輔元輔。

動詞加ing作謂語的情況

這時候的動詞加ing前面必須加上be動詞,形成be+動詞ing(現在分詞)作句子謂語，構成進行時態句子。

例如:

He is reading a book now.他正在看書。

He was watching TV when his mother came in.他媽媽進來時，他正在看電視。

They've been waiting for you for three hours.他們等你三個小時了。

動詞加ing做非謂語的情況

1.動詞作介詞的賓語要加ing(動名詞)

I'm looking forward to seeing you again.我期盼著再次見到你。

The boy is so excited about hearing from his mother.男孩為收到他媽媽的來信很興奮。

2.部分動詞用動詞做賓語，做賓語的動詞要加ing(動名詞)！

I Practising speaking English Every day.我每天練習說英語。

Could you mind opening the door?你介意開門嗎？

I have finished reading three books.我已經看完三本書。

The old man Enjoys living in the country.這老人喜歡住在農村。

3.一些固定句式后面要加動詞ing(現在分詞)。

We have fun Playing in the park on Sunday.

Most students have problems speaking English.

4.動詞修飾名詞做后置定語時，要加ing(現在分成)！There is a boy Crying over there.

I felt something moving in the house.

I heard someone singing in the next room.

5.動詞做主語和表語時，動詞要加ing(動名詞)。

Swimming is very popular in summer.

His job is teaching English.