单项选择题
In the first paragraph, Mark thought that（）
A．nobody was so able as to solve these problems B．many people were too selfish to think about others C．he was not in the position to solve such problems D．he already had more than enough work to do
单项选择题 21（）
填空题 划线部分不同的是（）
单项选择题 The forest fire caused by the volcano is difficult to be（）
