This is a book和This is a bag 和This is a pen和This is a pencil

This is a book和This is a bag 和This is a pen和This is a pencil This is a book This is a pen and ____ is a pencil. This is a pencil and a pen还是This are a pencil and a pen, a和an的用法This is( )book This is( )eraser This is( )Englishbook Is this a book?" "Yes,this is." This is a book and that is a pencil THIS BAG IS NOT A This is a pen,and ____is a pencil over there This is a pen.(this)are pencily this is a my pen Is this a your pen?