Решение:
Используем was для единственного числа и were для множественного числа.
- The day was very warm. (The day - единственное число)
- He was in the bedroom. (He - единственное число)
- The trees were yellow. (The trees - множественное число)
- My friends were at the theatre. (My friends - множественное число)
Ответ: The day was very warm. He was in the bedroom. The trees were yellow. My friends were at the theatre.