Virus is the main agent that is responsible for causing common cold. So the correct option in regards to the given question is option "D". Common cold can be very distracting for any person. The viruses causing common cold are not fatal in nature.This virus normally affects the upper respiratory tract and mainly is a cause for concern of the nose. The virus can have a nominal effect for up to ten days or can linger for about 3 weeks.About 200 types of viruses are held responsible for causing common cold in humans. The duration of the cold depends on the type of viral attack.
