单选题两个数a，b的几何平均值的3倍大于它的算术平均值． (1)a，b满足a 2 +b 2 <34ab(2)a，b均为正数

单选题已知y=2x+x2+e2，则y'等于{{U}} {{/U}} A.2x+2x+e2 B.2xlnx+2x+2e C.2xln2+2x D.x2x-1+2x

单选题设，则______．A．B．a=0，b=-2C．D．a=1，b=-2

单选题若数列{an}的前n项和Sn=n2，则A．B．C．D．E．1

单选题设f(x，y)为区域D内的函数，则下列命题中不正确的是(A)若在D内，有，则f(x，y)≡常数．(B)若在D内的任何一点处沿两个不共线方向的方向导数都为零，则f(x，y)≡常数．(C)若在D内，有df(x，y)≡0，则f(x，y)≡常数．(D)若在D内，有，则f(x，y)≡常数．

单选题某人驾车从A地赶往B地，前一半路程比计划多用了45min，速度只有计划的80%，若后一半路程的平均速度为120km/h，此人还能按原定时间到达B地，则A、B两地距离为______．

单选题If the areas of the three different sized faces of a rectangular solid are 6, 8, and 12, then what is the volume of the solid? (A) 576 (B) 288 (C) 144 (D) 48 (E) 24

单选题设D是第一象限由曲线2xy=1，4xy=1与直线y=x，围成的平面区域，函数f(x，y)在D上连续，则=______。A．B．C．D．

单选题设f(ex)=x，则函数f(x)在区间[1，2]上的平均值等于 A. ln2+1． B. ln2-1． C. 2ln2+1． D. 2ln2-1．

单选题There is virtually no limit to how one can serve community interests, from spending a few hours a week with some charitable organization to practically full-time work for a social agency. Just as there are opportunities for voluntary service (1) (VSO) for young people before they take up full-time employment, (2) there are opportunities for overseas service for (3) technicians in developing countries. Some people, (4) those who retire early, (5) their technical and business skills in countries (6) there is a special need. So in considering voluntary or (7) community service, there are more opportunities than there (8) were when one first began work. Most voluntary organizations have only a small full-time (9) and depend very much on volunteers and part-timers. This means that working relationships are different from those in commercial organizations, and values may be different. (10) some ways they may seem more casual and less efficient, but one should not (11) them by commercial criteria. The people who work with them do so for different reasons and with different (12) , both personal and (13) . One should not join them (14) to arm them with professional experience; they must be joined with commitment to the (15) , not business efficiency. Because salaries are (16) or non-existent many voluntary bodies offer modest expense. But many retired people take part in community service for (17) , simply because they enjoy the work. Many community activities possible (18) retirement were also possible during one's working life but they are to be undertaken (19) seriously for that. Retired people who are just looking for something different or unusual to do should not consider (20) community service.

单选题设且f(x)展开的正弦级数为，则S(3)=

单选题设α是△ABC的一个内角，满足sinα+则△ABC一定是()．(A)不等边的锐角三角形(B)直角三角形(C)钝角三角形(D)正三角形