The process of spermatogenesis and oogenesis is started
respectively at

The correct option is A Puberty and embryonic stage

Spermatogenesis
Spermatogenesis is the process of formation of sperms from spermatogonia in the testes in males. It starts at puberty.

Oogenesis
Oogenesis is the process of formation of mature female gamete from oogonia in the ovary in females.

Unlike spermatogenesis, oogenesis starts before birth at foetal stage. Oogonia divides mitotically to form primary oocytes inside the primary follicles during foetal life. No more primary follicles are formed after birth. The remaining process of oogenesis then resumes at puberty.

Menarche
The beginning of menstruation or the first menstruation is called the menarche. It occurs at puberty.

Menopause
Menstrual cycle ceases around $50$ years of age. It is called menopause. It occurs when no follicles are left in the ovaries or due to changes in the pituitary hormone productions.

Puberty
Puberty is a transitional period between childhood and adulthood. In this period secondary sexual characteristics appears and the person achieve fertility.

Embryonic stage
Embryonic stage is the period after implantation, during which all the major organs and structures are formed within the foetus.