this is an apple的an为什么不可以是a

is this an apple an orange__an egg This is an apple就an apple部分转换提问 this is an apple 和 this is apple 哪个语法是正确的 This is (an apple)打括号的地方提问 This is an red apple.写出正确的句子 This is an apple in English.的答句是什么 this is an apple.改成复数形式 This is an apple 变为复数句子 an,is,apple,this连词成句 this is an apple的an为什么不可以是a ls this an apple?的肯定回答是Yes,this is an apple.还是Yes,it is an apple.就是“this/that”的回答是“this/that”还是“it”.啊、到底是it is还是this啊 Is she an apple? These are an apple and a pear.还是This is an apple and a pear. This is an apple.的否定句,疑问句,肯定回答,否定回答.学This is an apple.的否定句,疑问句,肯定回答,否定回答. this is an apple中为什么要用不定冠词不用可不可以,能不能写成This is apple That is an apple的复数是什么 this is an apple怎么改为复数句 This is （an apple）对括号部分提问