4. The boys are playing football in the yard now. (yesterday; many times)

Перевод задания: Преобразуйте предложения, используя слова в скобках.

The boys played football in the yard yesterday. (Мальчики играли в футбол во дворе вчера.)

The boys have played football in the yard many times. (Мальчики много раз играли в футбол во дворе.)

Yesterday указывает на Past Simple; many times — на Present Perfect.