1.I ATE dinner at Kenneth’s house a few times before.

2.I RODE horses many times before.

3. JENNA BEGAN her science project.

4. BORIS WENT to try the new restaurant on Ottawa Street.

5.THE CHILDREN WERE very busy with their homework.​

1. I have eaten dinner at Kenneth's house a few times before.

2. I have ridden horses many times before.

3. Jenna has begun her science project.

4. Boris has gone to try the new restaurant on Ottawa Street.

5. The children have been very busy with their homework.

Объяснение:

Для образования этого времени нужно писать частицы have/has + глагол в 3-й форме.