4. Which of the following statements is true? a. Technical Information Releases and Announcements are published in the Internal Revenue Bulletin, and were always included in the Cumulative Bulletin. b. The IRS issues "Determination Letters" and publishes summaries of these letters in the Internal Revenue Bulletin; they are rarely reprinted in the Cumulative Bulletin. c. LEXIS/NEXIS is one of the leading computerized legal data bank services which affords the researcher-user access to the full texts of primary source materials. d. The editorial opinion included in the leading looseleaf tax services is an excellent substitute for authoritative sources of law since it is more direct and easier to understand