为什么要用this?

为什么要用this? 为什么要是give him this letter.为什么要用him 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 I believe that this house is for sale.请问这为什么要用that this? have you read this book?do you read this book?为什么疑问词要用have 而 Is this you pencil 为什么不能回答 yes,this is.而是要用Yes,it is. how much is does this belt?为什么要用does Is this your sister 答语为什么要用it is. Is Mike free this afternoon? 为什么要用一般现在时 英语翻译还有为什么要用this kind of This is an alarm clock 为什么要用an? What is this in english?为什么要用What is