Ferning of cervical mucus depends on:

Ans is a, i.e. EstrogenEstrogen is responsible for the secretion of cervical mucus and progesterone is responsible for making it thick and viscid. Under the influence of estrogen cervical mucus is copious, watery elastic (can be stretched) and when dried it shows a characteristic fern pattern. Under the influence of progesterone cervical mucus is thick, scarly, loses its stretchability and an drying does not show fern like pattern.* Now we have to choose between option b and c as both estradiol and estriol are derivatives of estrogen.* It is mentioned earlier that estradiol is the more potent form of estrogen, in fact it is the most potent estrogen and estriol the least. So obviously estradiol will be responsible for most of the physiological action of estrogen and is therefore the option of choice.