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:
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Answer:Water masses give a very robust representation of the thermohaline state of the ocean and ocean circulation. ... This water body shows extremely stable vertical stratification, and its water density changes from ~1,011 kg/m3 at the ocean surface to ~1,016 kg/m3 at 100‐m depth.
Explanation:
Answer:
When the rider is at the top of the roller coaster.
Solution a is the most acidic.
In a pH scale of 1 to 14, the smaller the pH is, the more acidic is. In opposite, the higher the pH is, the more alkaline it is. We call substances with pH below 7 as acid, and above 7 as alkali, while 7 as neutral.
Therefore, comparing the 4 solutions, solution a has the lowest pH, 3, so it is the most acidic.