Available options:
[a]. sterility;
[b]. sensitivity;
[c]. hyperthyroidism;
[d]. immunity;

Answer the following question given this paragraph: The study of viruses is known as virology and people who study viruses are known as virologists . Viruses infect and live inside the cells of living organisms. When viruses infect the cells of their host, they may cause disease. For example, viruses cause AIDS (Acquired immune deficiency syndrome), influenza (flu), chicken pox, and the common cold. Therapy is sometimes difficult for viral diseases. Antibiotics have no effect on viruses and only a few antiviral drugs are available for some diseases. One of the best ways to prevent viral diseases is with a vaccine , which produces immunity . But vaccines are available for only a few diseases. Q: What do vaccines produce to combat viral diseases? A:
Answer:
[d].