Which of the following medical conditions are caused by a virus?

The common cold is indeed caused by a virus, specifically by several different viruses such as rhinoviruses. It is characterized by symptoms such as a runny nose, sore throat, and cough, making it a prevalent respiratory illness. Understanding the viral nature of the common cold is essential because it helps in distinguishing it from other conditions that may have similar symptoms but are caused by different microorganisms, such as bacteria or allergens.

In contrast, strep throat is caused by the bacterium Streptococcus pyogenes, pneumonia can be caused by various pathogens including bacteria, viruses, or fungi, and allergies are immune system responses to various substances that are not caused by infections at all. This differentiation is crucial in determining the appropriate treatment and management strategies for each condition.