An astrophysicist compiles a database of various exoplanets of mass M M\,M and the orbital radii r r\,r of their close-in moons in circular orbits. The database is used to analyze the orbital frequency f f\,f of these moons. The data show that f f\,f is directly proportional to:
(Mr3)1/2\left(\frac{M}{r^3}\right)^{1/2}(r3M)1/2
(M3r)1/2\left(\frac{M^3}{r}\right)^{1/2}(rM3)1/2
(r3M)1/2\left(\frac{r^3}{M}\right)^{1/2}(Mr3)1/2
(Mr)1/2\left(\frac{M}{r}\right)^{1/2}(rM)1/2
