Reread this excerpt from The Call of the Wild. Still more surprising was the change wrought in Dave and Sol-leks. They were new dogs, utterly transformed by the harness. All passiveness and unconcern had dropped from them. They were alert and active, anxious that the work should go well, and fiercely irritable with whatever, by delay or confusion, ret*rded that work. The toil of the traces seemed the supreme expression of their being, and all that they lived for and the only thing in which they took delight.

What is the best description of Dave and Sol-leks, based on this excerpt?

They are difficult to please.
They are cheerful and energetic.
They are mature and experienced.
They are dedicated to their tasks.