Sentence Correction (SC) | Re: Geologists in California have discovered a fault

Geologists in California have discovered a fault near the famous San Andreas Fault, one that they believe to be a trigger for major quakes on the San Andreas.
(A) one that they believe to be a trigger for
(B) one they believe to be a trigger for
(C) one that they believe triggers
(D) that they believe to be a trigger for
(E) one they believe acts as a trigger for