Hello!
Your question asks what we can conclude about the alien's thoughts on the theologian's ideas.
The excerpt states that "our two voyagers nearly fell over with that inextinguishable laughter." Due to this, we can already eliminate two of the answer options: Dangerous and unreasonable. The voyagers do not seem to think that the theologian's ideas are unreasonable or dangerous; they act as if it is quite the opposite.
There is also no mention that the aliens agree with the theologian's ideas or that they think that the ideas are true.
This leaves us with one final option: hilarious. The excerpt thoroughly describes the alien's laughter, which likely means that the aliens found the theologian's ideas to be hilarious.
I hope this helps you!