This/These, That/Those

(a)   is a hippo.

(a)   are birds.

(a)   is a giraffe.

(a)   are elephants.

(a)   is a tiger.

(a)   are zebras.

(a)   is a bookcase.

(a)   is my classroom.

(a)   is my school.

(a)   is a rubber.