One who is ____________ gets on with his job in spite of obstacles, while the one who is __________ hardly shows any progress. The latter spends all his time ___________ about his troubles.

The first two blanks present a contrast between a person who works in spite of all the obstacles, and someone who hardly shows any progress. The words that portray these two people should be appropriately defined and should be antonymous with each other. The correct set of words to be used here is provided in option B. While 'assiduous' refers to someone who shows care and perseveres in spite of all the obstacles, 'querulous' is someone who complains and is petulant, 'whining' also means to cry and make sound (about one's troubles).

Option A does not use the right word for the last blank ('speaking'), the same is the case with option C ('gossiping'). Option D is incorrect because 'hotheaded' is not a positive word for the first blank where we define a person who gets on with their job despite obstacles.