Under Treasury Circular $230,$ which of the following correctly represents the requirements related to the communication of fee information from a tax practitioner to a taxpayer:

A$.$

It may not be communicated by television, radio, or hand$-$delivered flyers.

B$.$

It must be communicated as an estimate before the engagement begins, with the understanding that the actual amount of the fee will not be determined until the engagement ends.

C$.$

It may be communicated in a number of ways, including in professional lists, telephone directories, mailings, and electronic mail.

D$.$

It may be communicated only through the confidential engagement letter between the tax practitioner and the taxpayer.