Could we see a galaxy that is 20 billion light-years away? (assume that we mean a "lookback time" of 20 billion years.)

yes we could its just that the star is most likely dead when we see it i know we can see a star like this because even if the star dies the light is still traveling, like if you went on a drive away from your home and then your home is destroyed just as you leave, just because you house is gone does not mean you cant still travel.

i believe the answer would be:

d. violin, clarinet, french horn, and tuba

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.