This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Twin Pregnancy, Molar Pregnancy, Gestational Trophoblastic disease and contraception in special situations (Sour Grapes!), Subject name: Gynaecology & Obstetrics
Most common type of monozygotic twin pregnancy at 4th-8th day of cell division 
Select and explain. 
A. Monochorionic Monoamniotic twins with Siamese presentation, B. Monochorionic Monoamniotic(MO-MO) twins, C. Monochorionic Diamniotic twins(MO-DI), D. Dichorionic Diamniotic twins (DI-DI)
C: Monochorionic Diamniotic twins(MO-DI)
Answer: C: Monochorionic Diamniotic twins(MO-DI) 
Explanation: In monozygotic twins, chorionicity depends upon time of cell division. Time of cell division Chorionicity of placenta First 72 hours post feilization(morula stage) DCDA 4-8th day(blastocyst stage) MCDA(MC type of monozygotic twins) 8-12th day MCMA >12th day Conjoined/Siamese twins, type of MCMA(fusion of embryonic disc occurs)