为什么说This is my a pen是错的?

this is a my pen 是This is my blue pen 还是This is my a blue pen 新概念英语 不能说my this a pen?要说 my pen?为什么? What is this 是This is a pen.还是.It is a pen?为什么? 我的这一支钢笔 不能说my this a pen?要说 my pen? 1.This is my a pen.A为This B为my C为pen 问哪个是错误的- 并写出正确答案.A B C this is her pen的物主代词为什么是this pen is hers This is my a pen?对还是This is a my pen?对 this is my pen的同义句 this is my pen .改为意思相同的句子 this is a（ ） what's this?It's a pen.为什么不能说是"this is a pen.我们老师说就是不能说this This is my pen f_____Emma.