What do they mean by part of a “set”?

Which of the following are parts of a sphere

Analyze the graph of the cube root function shown on the right to determine the transformations of the parent function. then, determine the values of a, h, and k in the general equation.

Parabolas y=−2x^2 and y=2x^2 +k intersect at points a and b that are in the third and the fourth quadrants respectively. find k if length of the segment ab is 5.