the library is very big改为否定句:The library isn't very big. 有be 动词就在它后面加not
The library isn't very big.
be动词的否定式是在be动词的后面加上not,如:
He isn't a very good baseball player.
I'm not eating my lunch.
They aren't good baseball players.
希望我能帮助你解疑释惑。
The library isn't very big.
您好,把is改成isn’t