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 This is an orange An orange is orange this is an orange.( )oeange is ( ) orange It is( ).An orange is orange. This is a orange.It’s an orange.是否正确. It is an orange?还是Is it an orange? It is an orange eraser. An orange is orange是什么意思 Is it an orange?还是 Is it orange? orange is orange an orange is orange 那种说法对? It's(an orange)提问是What is this?