  We investigate the extraction of the rotational energy of a black hole under
different accreting environment. When the accretion rate is moderate, the
accretion disk consists of an outer thin disk and an inner advection-dominated
accretion flow. In such a combined disk, the outer thin disk can sustain a
magnetic field with moderate strength at the event horizon, leading to the
formation of relativistic jets with moderate luminosity and speed via the
magnetohrodynamic Penrose process. When the accretion rate increases enough, on
the other hand, the disk becomes geometrically thin near the horizon. In this
slim disk, the denser plasmas can sustain a stronger magnetic field than that
in a combined disk, leading to the formation of jets with greater luminosity
and speed via the Blandford-Znajek processs. It is discussed that the former
jets are associated with the Fanaroff-Riley (FR) I galaxies and the latter with
FR II galaxies.
