A Day's Lodging by Jack London (adapted excerpt)

He urged the dogs to their work again. He had travelled on the frozen surface of a great river. Behind him it stretched away in a mighty curve of many miles, losing itself in a fantastic jumble of mountains, snow-covered and silent. Ahead of him the river split into many channels to accommodate the freight of islands it carried on its breast. These islands were silent and white; no animals nor humming insects broke the silence; no birds flew in the chill air. There was no sound of man, nor mark of the handiwork of man—the world slept.

John Messner seemed succumbing to the apathy of it all as the frost was benumbing his spirit. He plodded on with bowed head, unobservant, mechanically rubbing nose and cheeks, and batting his steering hand against the gee-pole in the straight trail-stretches. But the dogs were observant, and suddenly they stopped, turning their heads and looking back at their master out of eyes that were wistful and questioning. Their eyelashes were frosted white, as were their muzzles, and they had all the seeming of decrepit old age, what of the frost-rime and exhaustion.

The man was about to urge them on, when he checked himself, roused up with an effort, and looked around. The dogs had stopped beside a water-hole, not a fissure, but a hole man-made, chopped laboriously with an axe through three and a half feet of ice. A thick skin of new ice showed that it had not been used for some time. Messner glanced about himself. The dogs were already pointing the way, each wistful and hoary muzzle turned toward the dim snow-path that left the main river trail and climbed the bank of the island.

"All right," he said. "I'll investigate. You're not a bit more anxious to quit than I am."

He climbed the bank and then disappeared. However, the dogs did not lie down, but on their feet eagerly waited his return. He came back to them, took a hauling-rope from the front of the sled. It was a stiff pull, but their weariness fell from them as they crouched low to the snow, whining with eagerness and gladness as they struggled upward to the last ounce of effort in their bodies. When a dog slipped or faltered, the one behind nipped his hind quarters. The man shouted encouragement and threats, and threw all his weight on the hauling-rope.

Which thematic idea does the passage develop?

A. overcoming fear of the unknown
B. completing a dangerous journey
C. the beauty of the great river
D. the dedication of sled dogs