How should the quotation marks in this sentence be revised?

In 1793 doctors still believed “that there were four humors—phlegm, choler, bile, and blood”—that controlled human health, a theory that dated back to ancient Greece.

Answer choices for the above question

A. Remove the quotation mark after blood and add a quotation mark after the period

B. Remove the quotation mark before that and add a quotation mark before believed

C. Remove the quotation marks

D. No change needs to be made to this sentence