Generally, a practitioner may not charge a contingent fee for services rendered in connection with any matter before the Internal Revenue Service. However, there are circumstances where a contingent fee is allowed. Which of the following statements is correct?

Question $2$Select one:

a$.$

A practitioner may not charge a contingent fee for services rendered in connection with the IRS' examination of$,$ or challenge to an original tax return

b$.$

A practitioner may charge a contingent fee for services rendered in connection with an amended return or claim for refund or credit where the amended return or claim for refund or credit was filed within $120$ days of the taxpayer receiving a written notice of the examination of$,$ or a written challenge to the original tax return

c$.$

A practitioner must charge a contingent fee for services rendered in connection with any judicial proceeding arising under the Internal Revenue Code

d$.$

All of the above are correct statements regarding contingent fees