Answer:
A.,15 to 20
Explanation:
The beginning stage of the most lasting part of labour during child birth can take up to 20 hours and it usually commences when the cervix of the woman starts to dilate and it ends when it is completely dilated. The tightening up of the muscle of the uterus (known as contraction) do get more intense as the time progresses and the mild contraction typically start at fifteen to twenty minutes apart, for a period of sixty to ninety seconds.