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: Gynaecology & Obstetrics
According to Hellin's law chances of twins in pregnancy are: 
Select and explain. 
A. 1 in 60, B. 1 in 70, C. 1 in 80, D. 1 in 90
C: 1 in 80
Answer: C: 1 in 80 
Explanation: According to Hellin’s rule
The mathematical frequency of multiple pregnancy is:

Twins 1 in 80
Triplets 1 in (80)2
Quadruplets 1 in (80)3 and so on