Can His Football Come Out
他的足球可以出來嗎？
George knocked on the door of his friend's house. When his friend's mother answered he asked,
喬冶敲著他朋友家的門。當朋友的媽媽來應門時，他問:
"can Albert come out to play?"
“阿爾伯特可以出來玩嗎？”
"No,"said the mother,"it's too cold."
“ 不行， ” 那位媽媽說， “ 天氣太冷了。 ”
"Well, then,"said George,"can his football come out to play?"
“ 噢，那么。”喬冶，“他的足球可以出來玩嗎？

1.Knock on
Knock on: 敲（門、窗等）
例句與用法:
1. He accidentally knocked on (the pass from Jones). 他非故意犯規, 用手向前擊了（從瓊斯傳來的）球.
2. Jim sat up when he heard the knock on his bedroom door. 吉姆聽到敲寢室門的聲音時便坐了起來。
3. Please do not enter before knocking on the door. 進來前請先敲門。
下面來區分一下knock at：
Knock at: vt. 敲 例句與用法:
1. There was a furious knock at the door. 有人在猛烈地敲門。
2. Did I hear a knock at the door? 是有人敲門嗎?
3. Did you hear the knocks at the door? 你聽到敲門聲了嗎

總而言之，這兩次詞的區別不是很大，有時可以通用，但是一般表示敲在人身上的某個部位習慣用knock on 而不是knock at .如: Knock on her head 等。

2.Come out
come out：出來；出現；出版；出獄
eg：How did the printing come out? 印刷是怎樣出現的？
Notice：come out這個詞組是沒有被動語態的。