What was one of the challenges doctor salk faced in his attempt to create a polio vaccine ?

The correct answer would be d.

Ibelieve the correct answer is  d. they bound logs together and built a raft. enkidu steered it down the great river. gilgamesh carried humbaba's head.we know that gilgamesh was triumphant in this battle because he is carrying his enemy's head. he defeated humbaba, and then decapitated him to have his head as a trophy, or to show it to everyone that he managed to defeat his enemy.