把下面的句子变成复数形式(1)This is a book.(2)That is a yellow pencil.(3)He is a good boy.(4)She is playing on the computer.

These are some books.
Those are some yellow pencils.
They are good boys.
They are playing on the computers.

1.These are books.
2.Those are yellow pencils.
3.They are good boys.
4.They are playing on the computers.

these are books.
those are yellow pencils
they are good boys
they are playing on the computer(s).