Which sentence is punctuated correctly?
AI understand that Dr Elliott earned his M.D. at Columbia University.
BI understand that Dr. Elliott earned his M.D. at Columbia University.
CI understand that Dr, Elliott earned his MD at Columbia University.
AI understand that Dr Elliott earned his M.D. at Columbia University.
BI understand that Dr. Elliott earned his M.D. at Columbia University.
CI understand that Dr, Elliott earned his MD at Columbia University.