单项选择题

A. Add a DataProtectionPermission attribute to the CreditCardNumber property and set the ProtectData property to true.
B. Convert the DataContract to a MessageContract and set the ProtectionLevel property to SignAndEncrypt.
C. Change the data type of CreditCardNumber from string to SecureString.
D. Implement the CreditCardNumber property getter and setter In the setter, run the value of the CreditCardNumber through the MD5CryptoServiceProvider class TransformBlock method.