What do Ralph and Simon's reactions to the discovery of "a sort of half-cave" on the castle rock reveal about their respective characters?
Ralph and Jack both get excited about the prospect of using the castle as a fort, which shows that, in spite of all their hardships on the island, the two are still both just boys who want to play and have fun.
Jack gets excited about the idea of using the castle as a fort, but Ralph immediately responds by pointing out the lack of a fresh water source. This shows that while Jack still wants entertain his wild side and play islander, Ralph has taken on the burden of leadership and thinks only of practical things like water and rescue.
Ralph focuses on the lack of a fresh water source, while Jack looks around until he finds a trickle of water. This shows that Ralph is becoming disheartened by his time on the island and is only able to see the negative, while Jack is becoming a problem solver who finds water, gets the group meat, etc.
Jack focuses on the lack of a fresh water source, while Ralph looks around until he finds a trickle of water. This shows that Jack is becoming increasingly negative and cruel as time wears on, while Ralph still maintains the light of civilization and attempts to find the good and useful side of everything.
None of the above accurately describes the boys' reactions and their meanings.