$(a)$ What is immunisation?
$(b)$ Categorise the following into acute,chronic,infectious,or non-infectious diseases: Typhoid,$TB$,Goitre,Elephantiasis.

Fill in the blanks:
$(a)$ Pneumonia is an example of . . . . . . disease.
$(b)$ Many skin diseases are caused by . . . . . . .
$(c)$ Antibiotics commonly block biochemical pathways important for the growth of . . . . . . .
$(d)$ Living organisms carrying the infecting agents from one person to another are called . . . . . . .

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

Explain the following statements:
$(a)$ Being disease-free is not the same as being healthy.
$(b)$ Community health is essential for good individual health.
$(c)$ Villagers suffer from cholera more than urban people.

About a hundred years ago,when smallpox persisted,a group of people who had this disease earlier and had survived it had no chance of suffering from it again. So,having the disease once was a means of preventing subsequent attacks of the same disease.
$(a)$ Why does this happen? Explain.
$(b)$ We can 'fool' the immune system. Clarify.
$(c)$ Name this principle of prevention of diseases.

Which one of the following is not important for individual health?