What is the central idea of "agassiz and the fish, by a student"?

  The correct answer is :  The central idea is the need to make an observation carefully, to look again and again and to be able to study the reality in front of us.

Explanation:  Agassiz was the founder of the Harvard Museum of Zoology and a professor there as well. The detailed observation that he ordered his student to make initially from a fish and then to make the comparison between many fish, cost the student a lot of work but finally he recognizes that it was a great legacy that his teacher left him.

the answer should be:

the intervention of the supernatural gives gilgamesh hope that he will defeat humbaba.