Где употреблять was а где were

I was

You were

He was

She was

It were

We were

They were

Was

were

He was a doctor.

I was in this country.

That city was beautiful.

The book was interesting.

The boy was swimming.

Mary was in the park.

I was playing the piano.

They were doctors.

We were in this country.

Those cities were beautiful.

The books were interesting.

The boys were swimming.

Mary and Tom were in the park.

We were playing the piano.