【阅读理解】Two United Nations agencies warned on Tuesday that children are most at risk of developing skin cancers as a result of the long-term decline in the earth's protective ozone layer. The agencies, the World Health Organization(WHO)and the UN Environmental Programme(UNEP), issued the warning as they launched a global programme aimed at alerting schools to the dangers of exposure to the sun.
Why does the risk of developing skin cancers in children become greater and greater?
A
Because they pay little attention to their skin health.
B
Because they are short of physical training.
C
Because the earth's protective ozone layer declines year after year.
D
Because the earth is getting warmer and warmer.
