Assuming Everything Else Is Constant, When a Stock Goes Ex-Rights

Assuming everything else is constant, when a stock goes ex-rights its price should:

A) decrease since the stockholder is losing an option.
B) increase since the corporation no longer has the right to force the stockholder to convert.
C) remain the same since an efficient market would anticipate this change.
D) move up or down depending on whether a small investor wanted to exercise his/his rights.
E) None of the above.