What is the major disadvantage of external Fertilization ?

Which reproductive adaptation is characteristic of most terrestrial vertebrates but not of most aquatic vertebrates?

Why the chances of survival of young ones is greater in viviparous ?

Which of the following statements are correct regarding female reproductive cycle?

$A$. In non-primate mammals cyclical changes during reproduction are called oestrus cycle.

$B$. 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.

Pair of chromosomes in maize