The correct answer is: B. Viruses.
Influenza is a respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can
lead to death. The best way to prevent the flu is by getting a flu vaccine each year.Bacteria are single-celled organisms that can cause a variety of diseases in humans, including pneumonia, strep throat, and food poisoning. Fungi are multicellular organisms that can cause diseases such as athlete’s foot, ringworm, and yeast infections. Algae are single-celled organisms that can cause diseases such as algal blooms.
Influenza is not caused by bacteria, fungi, or algae. It is caused by viruses. Viruses are much smaller than bacteria or fungi, and they can only replicate inside living cells. There are many different types of influenza viruses, and they can change over time. This is why it is important to get a flu vaccine each year, as the vaccine is designed to protect against the most common strains of influenza virus that are circulating.