Sure, let's identify the errors in the sentences:

31. The (A) herb (B) of buffaloes were grazing on the field.
- Correction: The error is in (A). The correct word should be "herd" instead of "herb".
- Corrected sentence: The herd of buffaloes were grazing on the field.

32. You should not (A) spend much (B) time play computer games (D).
- Correction: The error is in (C). The correct form should be "playing" instead of "play".
- Corrected sentence: You should not spend much time playing computer games.

33. The combine harvester makes (A) the process of harvesting (B) the rice much more quickl easier (D) for the farmers.
- Correction: The error is in (C). The correct form should be "quickly" instead of "quickl".
- Corrected sentence: The combine harvester makes the process of harvesting the rice much more quickly and easier for the farmers.