Вставь is,are. this a computer. those desks. these lamps. that a chair. it dan's rocking horse. they lida's toys.

This is
Those are
These are
That is
It is
They are

This is a computer.
Those are desks.
These are lamps.
That is a chair.
It is Dan's rocking horse.
They are Lida's toys.

Местоимения this , that и  it указывают на единственное число, то есть глагол is.
Местоимения these, those и they указывают на множественное число, то есть глагол are.