I am inclined to prefer your #3 and #4, but lt really would be a lot easier to answer your question if you gave the full sentences rather than denoting them by letters.
3. The reasons are: 1) A is B; 2) C is A; and 3) D is B. *A colon is added after "are."
4. The reasons are 1) A is B; 2) C is A; 3) D is B. *Omited the "and" at the end.[/QUOTE]
Student or Learner