(20 1 1? A classmate is standing on the elevator floor, studying the situation of a sightseeing elevator in the process of lifting with speed sensor and computer, as shown in the figure.

A, in 5s ~ 10s, the speed-time image is horizontal. At this time, the elevator is moving at a constant speed and in a state of force balance, so the pressure of the classmate on the elevator floor is equal to his gravity, so A is correct;

B within 0 ~ 5s, it can be seen from the speed-time image that the acceleration is positive and the elevator acceleration is upward. People are overweight at this time, so B is wrong.

C. at 10? In s ~ 20s, students decelerate and rise evenly, with constant acceleration and constant support. The supporting force has done positive work, and the mechanical energy of students is increasing, so C is wrong.

D, 20? During s ~ 25 s, the sightseeing elevator is accelerating and descending, and the acceleration of the elevator is downward. At this time, people are in weightlessness, so D is wrong.

So choose a.