A. Youthful
B and D is considered negative while C means they have had very little experience on something
(っ◔◡◔)っ ♥ Atank chu. I don't know what to say, but I hope your having an amazing day! ♥
From what i know B is going to be the best one of these options
The sentence would be "Over the years, the research group has seen that humpback whales often live and hunt together for years"
