单选题

　　[填句补文]Though little research has been carried out about how exactly the sunspot will negatively harm the health of the people. ________. So， scientists warn that people going outdoors should be careful to protect their exposed skin and eyes with clothes， umbrellas and sunglasses from the strong sunlight rich in ultraviolet rays.

　　A、Ionosphere is high above the earth.

　　B、If the lights in your house keep flickering， blame frequent sunspots.

　　C、According to a research conducted by the Russian scientists from 1957 to 1960， the frequency of earthquakes can be linked to the movement of the sunspots.

　　D、A paper published by a North Korea observatory says that sun storms may cause an increase in the incidence of heart disease and skin disease.