This is a pen.—English.中间填in of an a 哪一个

this is a my pen This is a nice pen. this is a pen对a pen提问— —this? What's this?——___.(①It's a pen.②This is pen.③This is an pen.④It's a pen.) This is a pen.(this)are pencily This a pen.that is a pen,什么 This is a pen.就划线提问 this is a pen.改为复数句 this is a pen改成一般疑问句 This is a pen.改为一般疑问句 is this a youe pen 怎样改错 This is a nice pen.的问句 This is a pen.(改为复数形式) this is a pen on English.改错 this is red a pen的提问 is this a pen?No it i(). This is a oeange pen对吗? is this a pen（变成陈述句）