Choose the best closing for a message requesting the receiver's support for a proposed change in a benefits plan.
a. please e-mail me at your earliest convenience with your decision.
b. contacting me by december 1 about your support of this new benefits plan will allow me to present this proposal at the next strategic planning session.
c. if you have any further questions about this new benefits plan, please do not hesitate to contact me.
d. we really need to implement this new benefits plan soon.