Billing method for contraception is -

Ans. is 'a' i.e., Cervical mucus method Cervical mucus method* The cervical mucus method is also called "ovulation method" or more commonly "Billings' ovulation method." This method is based on recognizing the changes that occur in cervical mucus due to the effect of estrogen and progesterone at different times of the menstrual cycle.* Just before that, at the time of ovulation, the mucus becomes more copious, clear, and slippery, resembling the white of a raw egg, and can be stretched slowly between two fingers. The vagina and vulva feel moist or wet. This persists for about 3 days. These are called "wet days"; the last day of wet mucus is called the "peak day." These days mark the peak of fertility