Answer:
C.
Step-by-step explanation:
I'm not completely sure. I haven't read Grandpa's Beat-up Banjo but in David and Goliath, David (young human) goes up against Goliath (really big giant). Goliath has a sword and shield but all David uses is a rock and a sling.
Everyone doubts that he'll win until he uses the sling to shoot the rock and at least knocks out Goliath, a goal none of the soldiers had been able to achieve.