Which of the following sentences uses words most effectively?

a. If you agree, please contact the Foundation and advise them that you are our company’s representative and that all future correspondence should be directed to you.

b. If you agree, please tell the Foundation that you are our representative and ask them to send all mail to you.

c. If you agree, please contact the Foundation and tell them that you are our company’s representative and that all future correspondence should be sent to you.

d. If you agree, please contact the Foundation and tell them that you are our company’s representative and request that they direct all future correspondence to you.