The movement of air mass in the case of Tornado can be described as :
(a) Forced vortex throughout
(b) free vortex throughout
(c) Forced vortex at the core and free vortex outside
(d) Free vortex at the core and forced vortex outside
(a) Forced vortex throughout
(b) free vortex throughout
(c) Forced vortex at the core and free vortex outside
(d) Free vortex at the core and forced vortex outside