what is the correct answer for this multiple choice question?

Which one is a viable option to build artificial gravity in future spaceships?

a. Rotating spaceships with spinning velocities of more than 50 rpm (rotations per minute)

b. Supermassive spaceships with masses comparable to that of Earth to produce similar gravity.

c. using gravity generators in the future spaceships

d. Rotating spaceships with spinning velocities of less than 10 rpm.

e. Stacked spaceships with gigantic masses.