Menstrual cramps are experienced with the onset of the menses because of strong contractions of the layer of the uterus.

The Answer is " the middle muscular layer".
The middle muscular layer of the uterus is also known as myometrium.
There are three layers of the uterus;
1) the outer layer known as perimetrium
2) the middle layer that is myometrium
3) the inner layer which is known as endometrium.
The middle layer is responsible for the uterine contraction and as a result, one have menstrual cramps.

The correct answer is c.