Which is a run-on sentence? If you want to avoid back pain, you should maintain
proper posture.
You must be going somewhere nice your outfit is so
elegant.
On Saturday nights, the roller skating rink plays disco
music.

The second sentence is a run-on sentence

Explanation: A run-on sentence is when two or more independent clauses (phrases that can stand on their own as a sentence)  are not connected properly. You can connect them with a comma, or a conjunction(and, so, etc)

The second sentence has two independent clauses, "you must be going somewhere nice" and "your outfit is so elegant". However, these aren't connected properly so the answer is the second choice.

the answer should be:

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