A rectangular solid, \(x\) by \(y\) by \(z,\) is inscribed in a sphere so that all eight of its vertices are on the sphere. If \(x, y\) and \(z\) are positive integers, and the radius of the sphere is \(\dfrac{\sqrt{14}}2,\) what is the volume of the rectangular solid?

A. 6
B. 11
C. 12
D. 18
E. 22

Answer: A

Source: GMAT Club Tests