A nebula is gas, dust, and other things that form and form some sort of clould like thing. It also looks cool because of the colors it produces. I'm sure you could do a web search to find more about it, I don't take astronomy hahaha
1. e) None of the above is necessarily true.
2.d) Without knowing the mass of the boat and the sack, we cannot tell.
It hardens because you are pressing it against something.
I think your question is incomplete because the distance between destination and departure point isn't given in the question
