In a Pregnant Woman, Conception Most Likely Occurred Approximately

In a pregnant woman, conception most likely occurred approximately

A) two weeks before the onset of her last menstrual period.
B) at the onset her last menstrual period.
C) two weeks after the onset of her last menstrual period.
D) at the time of her first missed menstrual period.
E) two weeks after the time of her first missed menstrual period.