How is modern Earth different from Earth over four billion years ago? Constantly bombarded with comets and asteroids
Little to no oxygen
High levels of ultraviolet radiation
Protective atmosphere

answer: although many types of viruses can cause a common cold, rhinoviruses are the most common culprit. a cold virus enters your body through your mouth, eyes or nose. the virus can spread through droplets in the air when someone who is sick coughs, sneezes or talks. theres your answer

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