阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。
Leaders of the World Health Organization say they are concerned about the air quality and
health efiects on citizens during a recent outbreak of heavy pollution in Beijing．Still，they said they
were unsure of the exact amount the air pollution takes on any person’s body，casting doubts on
local reports tying the area’s dirty air to particular cases of illness．
