a apple和an apple哪种写法正确?

half an apple 还是a half apple an apple and a half以及one and a half apple和half an apple分别用is this is an apple 和 this is apple 哪个语法是正确的 请问为什么苹果和鸡蛋要用,an apple、an egg 而不是a apple、a egg An apple is a fruit. an apple is a fruit 是a apple tree还啊an apple tree? a apple juice 对 还 是 an apple juice 对 是a apple tree还是an apple tree? 首字母填空what apple is not an apple?A What a delicious apple还是What an delicious apple? Has she an apple.和Does she have apple.