If you live in an overcrowded and poorly ventilated house,it is possible that you may suffer from which of the following diseases?

What is immunity?

State whether the following statement is true or false:
Social equality and harmony are necessary for individual health.

We should not allow mosquitoes to breed in our surroundings because they :

$AIDS$ cannot be transmitted by:

Given below are a few situations:
$(i)$ Geeta of Class $IX$ was having a common cold. She sits with Sarika,who also develops the disease.
$(ii)$ Animesh of Class $IX$ shifted to a new residence with his family where a water purification system has not been installed yet. He develops Cholera and Dysentery.