The correct answer is D. You are infected by a virus.
Antibiotics are medications that are used to treat bacterial infections. They work by killing or stopping the growth of bacteria. Viruses are not bacteria, so antibiotics do not work against them.
When you have a sore throat and a runny nose, it is most likely that you have a viral infection. Viral infections are very common and usually go away on their own within a week or two. There is no need to take antibiotics for viral infections, because they will not help and may actually make you sicker.
If you have a sore throat and a runny nose, you can try to relieve your symptoms by drinking plenty of fluids, getting plenty of rest, and taking over-the-counter pain relievers. You can also try using a humidifier or taking a hot shower to help loosen mucus.
If your symptoms are severe or do not improve after a week or two, you should see a doctor. The doctor may be able to prescribe medication to help relieve your symptoms or to rule out a bacterial infection.