The period of adolescence is.........

If the number of chromosomes in most body cells of a mammal is $40$,the cells in the seminiferous tubule will have

The figure given below shows the sectional view of an ovary. Select the option which gives the correct identification of the marked structure ($A$ to $D$) and its feature.

Fertilisation of an egg cell means......
$(1)$ End of the process of oogenesis
$(2)$ Induces the completion of the second meiotic division
$(3)$ The corpus luteum degenerates
$(4)$ Signals for maintaining progesterone levels in the blood
$(5)$ Formation of a zygote

Which of the following statements are correct regarding the female reproductive cycle?
$A$. In non-primate mammals,cyclical changes during reproduction are called the oestrus cycle.
$B$. The first menstrual cycle begins at puberty and is called menopause.
$C$. Lack of menstruation may be indicative of pregnancy.
$D$. Cyclic menstruation extends between menarche and menopause.
Choose the most appropriate answer from the options given below.

Composition of semen is