Question

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

Answer 1

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

Answer 2

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.