A planetary gear train is gear train having
(a) a relative motion of axes and the axis of at least one of the gears also moves relative to the frame
(b) no relative motion of axes and no relative motion of axes with respect to the frame
(c) no relative motion of axes and the axis of at least one of the gears also moves relative to the frame
(d) a relative motion of axes and none of the axes of gears has relative motion with the frame
I have been asked this question by my college professor while I was bunking the class.
This intriguing question comes from Standard Spur Gears-1 in chapter Toothed Gearing & Gear Trains of Machine Kinematics