thatisapen改成否定句为

That isn't，在that is的is后面加not就是否定形式。that is在英语中很常见，例如:that is an apple.那是一个苹果。

that isn't a tomato.那不是西红柿。

that is a pencil.那是一个根铅笔。

that isn't a pen.那不是钢笔。

that is cat.那是一只猫。

that isn't a dog.那不是狗。