The Moons of Mars,Phobos (Fear)and Deimos (Terror),are Very Close to the Planet

Multiple Choice

The moons of Mars,Phobos (Fear) and Deimos (Terror) ,are very close to the planet compared to Earth's Moon.Their orbital radii are 9,378 km and 23,459 km respectively.What is the ratio of the period of revolution of Phobos to that of Deimos?

A) 0.2528
B) 0.3998
C) 1.582
D) 2.858
E) 3.956