The correct answer is (a). Hepatitis B is caused by a DNA virus called hepatitis B virus (HBV). HBV is a small, enveloped virus that is transmitted through blood and body fluids. It can cause acute hepatitis, which is a short-term inflammation of the liver, or chronic hepatitis, which is a long-term inflammation of the liver. Chronic hepatitis B can lead to serious liver problems, such as cirrhosis and liver cancer.
(b) RNA viruses are viruses that have RNA as their genetic material. RNA viruses are responsible for a variety of diseases, including influenza, measles, and HIV.
(c) Bacteria are single-celled organisms that are not viruses. Bacteria can cause a variety of diseases, including pneumonia, strep throat, and food poisoning.
(d) Platyhelminths are flatworms that can cause a variety of diseases, including tapeworm infection and schistosomiasis.