Provide definitions/explanations for the following terms: $1$. Retrovirus,$2$. Antibody.

(N/A) $1$. Retrovirus: These are viruses that contain $RNA$ as their genetic material. They use the enzyme reverse transcriptase to convert their $RNA$ into $DNA$ inside the host cell.
$2$. Antibody: These are a class of proteins known as immunoglobulins $(Ig)$,which are produced by $B$-lymphocytes in response to specific antigenic stimulation to neutralize pathogens.