单项选择题
A．because the earth is being polluted day and night B．thanks to science development C．because of the rise in population D．because the earth is blown away by the wind every years
A．Dangerous Sports--What and Why B．The Boredom of Modem Life C．Bungee Jumping--Is It Really Dangerous D．The Need for Excitement
A．positive B．negative C．neutral D．nervous