Как получается сумма коэффициентов 5 при диссоциации ортофосфата натрия

Use the correct-form.

1) He .... his workyeterday evening

a) does   b) is doing    c) did

2) They usually ....  to the seaside   in summer.

a) go     b) is going    c)   went

3) The childeren ..... the excursion lasy Sunday.

a)   enjoy    b)  enjoys  c) enjoyed

4) Look! The childeren.....in the like.

a)  swim    b)  are swimming   c)  swam