When an object vibrates in simple harmonic motion in the vertical direction, its minimum speed occurs when it

is at the lowest pointis

at the equilibrium point

is at either endpoint

is at the highest point

When an object vibrates in simple harmonic motion in the vertical direction, its minimum speed occurs when it is at either endpoint ... either the highest point or the lowest point.  

At those points, it reverses its direction, so its speed is zero for an instant.

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.