12. The chief engineer was instructing all the workers.of the plant

=> All the workers of the plant were being instructed by the chief engineer.

13. The students were learning English at 8 am yesterday

=> English was being learned by the students at 8 am yesterday.

14. What were you watching between 8 and 9 o'clock last night?

=> What was being watched by you between 8 and 9 o'clock last night?

15. Was Nam eating the Fried Chinese Rice when you arrived?

=> Was the Fried Chinese Rice being eaten by Nam when you arrived?

16. Were the scouts collecting the broken glass for recycling at tis time last month?

=> Was the broken glass being collected by the scouts for recycling at tis time last month?

17. Which sport were you playing at 4 o'clock yesterday afternoon?

=> Which was sport being played by you at 4 o'clock yesterday afternoon?

18. They weren't planting rubber trees in the forest at 9 am last Saturday

=> Rubber trees in the forest weren't planted by them at 9 am last Saturday.

19. Was your mother making tea at 10 o'clock last night?

Was tea made by your mother  at 10 o'clock last night?

20. Arthur was teaching vocabulary from 7 to 10 last night.

=> Vocablulary was being taught by Arthur from 7 to 10 last night.

12.  All the workers of the plant were being instructed by the chief engineer.

13. English was being learned by the students at 8 am yesterday.

14. What was being watched by you between 8 and 9 o'clock last night?

15. Was the Fried Chinese Rice being eaten by Nam when you arrived?

16. Was the broken glass being collected by the scouts for recycling at tis time last month?

17.Which was sport being played by you at 4 o'clock yesterday afternoon?

18. Rubber trees in the forest weren't planted by them at 9 am last Saturday.

19. Was tea made by your mother  at 10 o'clock last night?

20. Vocablulary was being taught by Arthur from 7 to 10 last night.