This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
What is the effect of Progesterone-only pills? 
Select and explain. 
A. Completely suppresses ovulation, B. Thin lining of uterus, C. Thick cervical mucus, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Ref. KDT. Page. 343
Progestogen-only pills have multiple biological effects on the female body.
Multitude effect of POP:

Inhibition of follicular development
Inhibition of ovulation
Suppression of corpus luteum formation
Changes in the nature of the cervical mucus which inhibits the passage of sperms into the uterine cavity – Thickening of cervical mucous secretion
Effects on the endometrium which affect implantation – by making it thin