Wǒ yǐjīng qù guò yí cì Běijīng le 。
I have been to Beijing once.
Wǒ gāngcái qiāo le jǐ xià mén ，dànshì méiyǒu rén lái kāi 。
I knocked the door once or twice just now but no one opened it for me.
Wǒ děi qù yí tàng xuéxiào 。
I have to go to school.
Nǐ kěyǐ zài shuō yí biàn ma ？
Can you repeat it again?
“我去北京” happened once, so we can use “次”.
“吃北京烤鸭” happened once in past, and it could happen again in the future.
We can say,
I have eaten Beijing Roast Duck once and I want to have a try again in the future.
“敲” may happened in a very short time. Such movements include “打” and “拍”. When such movements happen, we can use “下”.
He suddenly patted his younger sister on the back. His younger sister was very angry and she stroke him a lot.
“一下” can also be a phrase to show the time is short and to show some trial.
Could you please do me a favor?
“去一趟学校” emphasizes “去的过程”, and it is always used to describe the movements of going and coming.
After work, I want to go to the supermarket.
It is not easy for you to come. Why do you go back so early?
“说一遍” emphasizes that the whole process has been completed. The object for “说” is the “句子” with some length.
This song is so nice and I have listened to it for many times.
Please accompany me to watch the movie again.
Zhè běn shū xiě de tài hǎo le ，wǒ yǐjīng kàn le sān _____le 。
Zhēn bù hǎoyìsi ，qǐng děng wǒ yí ______。
Yīshēng shuō ，zhèxiē yào měi tiān chī sān ______，měi _______yí piàn 。
Zhōumò wǒ děi qù yí ______Shànghǎi 。
Zěnme zhème chǎo ？Nǐmen gāngcái shì bú shì zài qiāo zhuōzi ？
Lǎoshī ，wǒ zhǐ qiāo le liǎng ________。
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