Imagine that alien astronomers once lived on Venus and studied Earth. With their perpetually cloudy skies they could never see Earth with optical telescopes, but they could study it with radar particularly when Venus was close, between the Sun and Earth. Sending very short pulses at a fixed frequency they looked the shape of the returned pulses in both time and frequency. At this earlier time in Earth history our planet was almost totally covered with water and had just two small continents that were strong radar reflectors. One was at the South Pole and the other near the equator (Hawaii) and essentially all of the returned radar signal came from exposed land and not the ocean. During the Earth day, the Venusians sometimes saw the radar returns as double pulses in time and frequency.

Explanation:

find the solution below

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.

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.