Answer:
He fears they will not be able to take care of him and the other dogs
Explanation:
Why is Buck concerned about being with Hal, Charles, and Mercedes
Buck is concerned about being with Hal Charles, and Mercedes because he knows that they are incompetent and not fit to lead a sled of dogs.
The trio are inexperienced about handling dogs on a sled and Buck is worried and concerned because he fears he and the other dogs in the sled will not be taken care of.
