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.
正确答案：D
答案解析：这一段说的是太阳黑子对人类健康的影响。填入的内容也应该与健康有关，空格后一句说到要保护皮肤。因此D是正确的。