A is not the answer as he does not seem disappointed, instead is "happy with a new approach"
C isn't the answer as he wasn't frustrated to begin with
D is probably not the answer as all we know about is the new approach that he has come up with and we don't know if he has 'learned' to do what the option says.
In my opinion, B seems like the best option as he willingly asked Bob if he could coach rather than keeping things the way they were.
