she is a teacher.变复数 it is a pen.变复数 this is my

she is a teacher.变复数 it is a pen.变复数 this is my she is a teacher.变复数 This is pen变复数 Is this a pen?（变复数句） This is a pen变为复数句,怎么变 this.is pen变复数句 is she a housewife变复数 This is a photo of my family.变复数 this is a new car.变复数 this is a piano怎么变复数 This is a knife.怎样变复数. This is a marker.（变复数）