Ответ:

1. a) We listened to the girls singing Russian folk songs.

b) We listened to the Russian folk songs sung by the girls.

2. a) The girl washing the floor is my sister.

b) The floor washed by Helen looked very clean.

3. a) Who is that boy doing his homework at that table?

b) The exercises done by the pupils were easy

4. a) The house surrounded by tall trees is very beautiful.

b) The wall surrounding the house was very high.

5. a) The girl writing on the blackboard is our best pupil.

b) Everything written here is quite right.

6. a) Read the translated sentences once more.

b) The pupils translating  a very difficult text are tired.

Объяснение: