The hunter-gatherer birth spacing interval is primarily the result of:
a. nutritional stress
b. breastfeeding and child-rearing techniques
c. contraceptive practices
d. high infant mortality rate

b. Breastfeeding and child-rearing techniques were followed by the hunter-gatherers for the birth spacing interval.

Explanation:

The birth spacing interval among hunter-gatherer population was simply achieved by mother’s breastfeeding pattern and child-rearing and weaning techniques without the use of any contraceptives.

Mothers breastfed their infants nearly for the first two years of infancy. The constant round-the-clock sucking of the infants during breastfeeding led to hormonal changes leading to suppression of ovulation in a lactating mother.

Among nomadic hunter-gatherer groups, women carried their infants in a pouch on their backs while the men went for hunting. So close birth spacing required the mother to carry, wean and rear both the children at one time which would cause a heavy burden for the mother. Further, the energy expenditure during pregnancy and lactation also has to be covered.

Hence, the mothers breastfed the infant for longer periods which helped them in birth spacing.

menstruation is a process in which blood and mucous flows out every month through the vagina. this process occurs every month because one egg is released from the ovary every month and at the same time, the uterus (womb) prepares itself to receive the fertilized egg.

explanation:

hope this

d, i believe because of it's activity level