Which one of the following is not a viral disease?

Choose the wrong statement.

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.

Your younger brother observes some mosquitoes sucking juices of cut fruit pieces,though it is common knowledge that mosquitoes suck blood of humans. How will you explain this behaviour to him?

Which of the following can make you ill if you come in contact with an infected person?

Differentiate between infectious and non-infectious diseases (any three differences).