Using Naegele's Formula for Calculating the Expected Date of Birth

Using Naegele's formula for calculating the expected date of birth involves:

A) adding 9 months from the time of the last menstrual period.
B) adding 9 months from the time of the last menstrual period and subtracting 7 days
C) subtracting 3 months from the first day of the last menstrual period,then adding 7 days.
D) subtracting 3 months from the first day of the last menstrual period.