this is an orange.it is orange.为什么第一个加an,而第二个不加an

this is an orange.it is orange.为什么第一个加an,而第二个不加an It is( ).An orange is orange. It's(an orange)提问是What is this? It is an orange?还是Is it an orange? it is (black and white)画线提问.this is an orange orange.(一般疑问句）（）it green?NO,it(). This is a orange orange.This is an orange orangeThis is a orange orange.This is an orange orange.请问哪句正确? it's an orange意思it's an orange 什么意思?what's this in english?is an orange【这句什么意思？】 This is an orange orange.的同义句 What is this?it is orange. This is an orange改为复数句 This is an orange.改为复数句. this is an orange改复数句 This is an orange改为复数句 This is an orange .[改为复数句] is this an orange?(做出否定回答) —Is this an orange?— Yes,it is.哪里错了 this,it,an,what,is,orange,is,fox怎么连词成句 this it an what is orange is fox怎么连在一起?成一句话谢谢了,