What should be done to obtain a pure line of animals?

Discuss briefly how pure lines are created in animal husbandry.

Assertion $A$: Milk is a useful product used as a valuable food.
Reason $R$: It is the fresh natural secretion of the mammary glands of female mammals for the nourishment of their young ones.
Which option is correct for Assertion $A$ and Reason $R$?

Which of the following points is $NOT$ associated with the management of the dairy industry?

Which animal makes a significant contribution to milk production in our country?

What is the average fat content of buffalo milk (in $\%$)?