When the boys .......their hands,they. down at the table.(wash,sit)поставте в подходящей

When the boys washed their hands, they sat down at the table.

This sentence is in Past Indefinite. Past Indefinite is used for past action.

Verbs in English are divided into two groups. They are regular verbs and irregular verbs. We form Past Indefinite with the help of the suffix ed. We add this suffix to regular verbs. To wash is a regular verbs, thats why we use the suffix ed washed.

We use the second form of irregular verbs in Past Indefinite. To sit is an irregular verb. Thats why we use its the second form sat.