Answer:
D. They realize that he is the only person who is willing to participate
Explanation: Because he has a lot of determination.
Charlie is chosen for the experiment because he is a hard worker who desperately wants to learn, despite the many setbacks and limitations he encounters. The researchers know this because Ms. Kinnian vouches for him.
The answer is gerund because golfing ends in ING
Hrothgar asked Beowulf to battle Grendel's mother because the king believed he was the only man capable of dealing with such monsters. This was because Beowulf had earlier succeeded in mortally wounding Grendel. Further, Hrothgar wanted revenge for his close friend.