Responding to the public's fascination with-and sometimes
undue alarm over-possible threats from asteroids, a scale
developed by astronomers rates the likelihood that a particular
asteroid or comet may collide with Earth.
A. a scale developed by astronomers rates the likelihood
that a particular asteroid or comet may
B. a scale that astronomers have developed rates how
likely it is for a particular asteroid or comet to
C. astronomers have developed a scale to rate how likely
a particular asteroid or comet will be to
D. astronomers have developed a scale for rating the
likelihood that a particular asteroid or comet will
E. astronomers have developed a scale that rates the
likelihood of a particular asteroid or comet that may.

IMO:[spoiler]C, what is your take? and what is OA?[/spoiler]