Answer:
b
Step-by-step explanation:
if the stone was some sort of reward then b would make more sense
if the stone was something precious or valuable to someone and have to trust it to someone and no one was an option then it would be a, but that kinda sounds weird so i thought it was probably b. another reason why it's probably b is cause c doesn't make much sense unless somebody stole it or something, which leaves d, but that doesn't sound like a good theme or lesson cause if it was something helpful you shouldn't keep it to yourself