The answer here is D, and it's kind of obvious. But you probably already knew the answer and are just doing this for piece of mind.
Explanation: Just the fact that we don't know whether or not there even is extraterrestrial life rules out every other answer, without even needing to go in depth.
(Okay, I read your question completely wrong, it's asking for which one of these has been solved isn't it?)
This is tough because all of these other than D have been figured out. Go with the methane atmosphere then.
Answer: Options A, B, C, D at correct
Explanation:
Cnidarians are a branch of invertebrates characterised by by a radially symmetric body including a saclike internal cavity and nematocysts; stinging structures that aids in feeding. They are also known as coelentrates. They are diploblastic (2 body layer). They also reproduce asexually by various mean including budding. Example include sea anemones, hydra, corals, jellyfish etc
The correct answer is D.
Hope this helps, and Brainliest answer would be appreciated!
Answer:
scientific theory is the answer
