[单选题]平流层对航空活动有利的方面是:
A. 气流平稳、无恶劣天气、发动机推力增大
B. 气温低、飞机载重量增加、飞机真空速增大
C. 气流平稳、能见度好、空气阻力小

[填空题]彩版文件生效前在（）个工作日内完成培训

[简答题]Americans today don’t place a very high value on intellect. Our heroes are athletes, entertainers, and entrepreneurs, not scholars. (1) Even our schools are where we send our children to get a practical education—not to pursue knowledge for the sake of knowledge. Symptoms of pervasive anti-intellectualism in our schools aren’t difficult to find. "Schools have always been in a society where practical is more important than intellectual," says education writer Diane Ravitch. "Schools could be a counterbalance." Ravitch’s latest book, Left Back: A Century of Failed School Reforms, traces the roots of anti-intellectualism in our schools, concluding they are anything but a counterbalance to the American distaste for intellectual pursuits. But they could and should be. Encouraging kids to reject the life of the mind leaves them vulnerable to exploitation and control. (2) Without the ability to think critically, to defend their ideas and understand the ideas of oth