62.. What have Americans achieved in environmental protection?
A. They have cut car emissions to the lowest
B. They have settled their environmental problems
C. They have lowered their CO levels in forty cities.
D. They have reduced pollution through effective measures.
61. Where does the support for environmental protection mainly come from?
A. The grass –roots level B. The business circle
C. Government officials D. University professors
60. According to Anderson, before 1970, Americans had little idea about ___
A. the social movement B. recycling techniques
C. environmental problems D. the importance of Earth Day
22. 函数.
(1)讨论的单调性;
(2)设,证明:.
21. 已知抛物线:的焦点为,直线与轴的交点为,与的交点为,且.
(1)求的方程;
(2)过的直线与相交于、两点,若的垂直平分线与相交于、两点,且、、、四点在同一圆上,求的方程.
20.设每个工作日甲、乙、丙、丁人需使用某种设备的概率分别为、、、,各人是否需使用设备相互独立.
(1)求同一工作日至少人需使用设备的概率;
(2)表示同一工作日需使用设备的人数,求的数学期望.
19.如图,三棱柱中,点在平面内的射影在上,,.
(1)证明:;
(2)设直线与平面的距离为,求二面角的大小.
18. 等差数列的前项和为,已知,为整数,且.
(1)求的通项公式;
(2)设,求数列的前项和.
三、解答题
17.的内角、、的对边分别为、、,已知,,求.
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