Вспомни формы Past Simple глагола to be. Professor ... here ten days ago. I...In London last week. We...at school yesterday.

Глагол to be в прошедшем времени Past Simple имеет форму was для единственного числа (I, she, he, it) и форму were для множественного числа (we, you, they) и 2-ого лица единственного числа (you).

Professor was here ten days ago. I was in London last week. We were at school yesterday. He was at the airport yesterday.