Which do you think is more likely: humans visiting an alien planet or aliens from another planet visiting us?

What is the problem in this article? what solution does the article propose?

What's the waste product of electrons and pyruvate combining in fermentation?  

What causes eclipses? check all that apply. earth's rotation on its axis moon's shadow covering the sun earth's shadow covering the moon earth's orbit and moon's orbit occasionally aligning the moon and sun's gravity pulling in the same direction