Which one of the following has a long-term effect on the health of an individual?

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

Give any four reasons to justify why it is more difficult to prepare antiviral medicines than antibiotics.

Students of class $IX$ had to present a seminar on 'Dengue fever'. They wanted to introduce the disease by starting with:
$(a)$ Immediate causes of the diseases
$(b)$ Definition of infectious diseases
$(c)$ Pathogen causing dengue fever
$(d)$ Vector responsible for dengue microbe.
Can you help them to explain the above points? Give details.

How can we prevent water-borne and vector-borne infections?

State whether the following statement is true or false:
The diseases which last for only short periods of time are called chronic diseases.