“There is an apple”（这是一棵苹果树）中为什么用“an”?

There is an apple on the There is an apple in his hand there is an apple in the tree . There is an apple and two pens There are an apple and two pens 哪个对 there is an apple.分析结构 到底there是主语还是Apple是主语 there is an apple on the table.it is yours there is an apple ____ _____on the table there is an apple on the table 改为复数形式 There is an apple in my hand.(变成同义句) There is an apple on the tree.(改为复数） is there an apple on the table?否定回答 Is there in tree apple an the连词成句 is there an apple on the table.否定句 There is an apple on the table.否定句 There is an apple in the box.变复数句 There is an apple in the box.改成否定句 is,apple,tree,there,an,here连词成句英语 There is an apple in the basket.改为否定句. there is an apple on the desk同义句.