When a block quotation is used in a research paper, punctuation the parenthetical citation.
a. is omitted from
b. is set off by a comma from
c. precedes
d. follows

I would say that punctuation, ie a comma , would precede the block quotation to set it apart and then quotation marks would be used to show that it is a quotation, both at the beginning and end of the passage. Quotations are good to show exactly what the author quoted meant so there is no doubt and which can then be accurately commented on.

It would be