What causes an un-proportionally thin and high tooth in the toe region, and a short and thick tooth at the heel?

Difference in PCDs of the generating gears

Error in indexing while manufacturing

Difference in outer and inner circumference of the generating gear

What causes an un-proportionally thin and high tooth in the toe region

1.	What causes an un-proportionally thin and high tooth in the toe region, and a short and thick tooth at the heel?
A.	Difference in PCDs of the generating gears
B.	Error in indexing while manufacturing
C.	Difference in outer and inner circumference of the generating gear
D.	Difference in feed rates
Answer» D. Difference in feed rates