32.Mary will see her friends off at the station.
=> Mary's friends will be seen off at the station
33.Workers were digging a large hole in the ground.
→.A large hole was being dug  in the ground by workers
34.Countries are finding a way to solve the problem.
→A way to solve the problem is being found by countries
36.The chief engineer was instructing all the workers of the plant..
=> All  the workers of the plant. were being instructed by the chief engineer
38.They will hold the meeting before May Day.
 The meeting will be hold  before May Day.