Read the following sentences and choose correct sentences

$1.$ Dysentery, plague, diphtheria are caused by bacteria

$2.$ Salmonella typhi directly affect the respiratory system

$3.$ Amoebiasis and Ascariasis are caused by contaminated water

$4.$ Internal bleeding, anemia muscular pain are symptoms of elephantiasis

In the given flow diagram, the replication of retrovirus in a host is shown. Observe and answer the following questions.

$(a)$ Fill in $(A)$ and $(B)$

$(b)$ Why is the virus called retrovirus ?

$(c)$ Can the infected cell survive while viruses are being replicated and released ?

$AIDS$ day is

$X-$rays are used in

‘Bacillary dysentery' is caused by