Which of kepler's laws describes the relationship between the average distance of a planet from the sun and the time the planet needs to make a revolution around the sun?
a. the law of gravity
b. the law of periods
c. the law of ellipses
d. the law of equal area and equal time

From the choices listed, "the law of periods" is the best choice,
although it's more commonly called the "law of harmonics".

It says that

           (the orbital period)
divided by
           (the cube of the half-major-axis of the orbit's ellipse)

is the same number for every planet in the solar system.