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: Social & Preventive Medicine
Mechanism of action of an oral contraceptive containing a combination of oestrogen-progestin is the following except-a) Inhibition of ovulationb) A change in the cervical mucusc) Inhibition of motility of the uterine tubesd) Inhibition of motility of spermse) Changes in the uterine endometrium 
Select and explain. 
A. ab, B. cd, C. bd, D. ac
B: cd
Answer: B: cd 
Explanation: None