i donts have a sister正確.你的問題牽扯名詞表類別問題.
a/an加可數(shù)名詞單數(shù)
A cat is a domestic animal.貓是家養(yǎng)動(dòng)物
零冠詞加可數(shù)名詞復(fù)數(shù)
Cats is domestic animals.
the表示人或事物的類別
The cobra is dangerous.眼鏡蛇是危險(xiǎn)的
If you park your car in the worng place,a traffic policeman will soon find it.一旦你把汽車停錯(cuò)了地方,交警很快就會(huì)發(fā)現(xiàn).