that is an apple.改为否定句that isn,t an apple为什么要用that isn,t. 从肯定句改为否定句,即是 把 是 改为 不是. That is 那是 改为 That is not 那不是. is not 的缩写 是 isn't 所以:that is not = That isn't 了. 很希望我的回答会对你有帮助.如有不明白,可以再追问,
