That's his pencil--box.(该为复数形式)

问题描述:

That's his pencil--box.(该为复数形式)

That are his pen--boxes.

Those are their pencil -boxes.

Those are their pencil-boxes.

That's his pencil-boxes.

These're their pencil-boxes

若只把pencil-box改为复数,则:
Thoese are his pencil-boxes.
若把整句都改为复数,则:
Thoese are their pencil-boxes.

Those are his pencil-boxes.