题目

如图甲所示，两个平行金属板P、Q竖直放置，两板间加上如图乙所示的电压，t=0时，Q板比P板电势高5 V，此时在两板的正中央M点有一个电子，速度为零，电子在电场力作用下运动，使得电子的位置和速度随时间变化。假设电子始终未与两板相碰。在0<t<8×10-10 s的时间内，这个电子处于M点的右侧，速度方向向左且大小逐渐减小的时间是(   ) A.0<t<2×10-10 s B.2×10-10 s<t<4×10-10 s C.4×10-10 s<t<6×10-10 s D.6×10-10 s<t<8×10-10 s More and more people believe that technologies are great for learning. Today, teaching tools like iPads are used in a lot of courses, i 1. language, history and science. Many teachers are supporters of using iPads in language learning. They say that students now have much more time for discussion in the classroom. Instead of spending valuable class time listening to texts or watching teaching videos. students can do this on their own and come to class prepared for discussion. The teachers also say that iPads allow students to learn at their own pace. Some students might listen to a dialogue only once and understand it. so they can save time for doing other things. Other students. however. might need to listen to the same dialogue again and again to understand it. Using iPads is especially h 2. to the students who are learning a language at different paces. The students who are using the new tool in some courses are also happy. They believe that using iPads is a more enjoyable way to learn(like listening to stories and watching movies). The class has become much more interesting and creative. There are other advantages for students. By using iPads, they can pay more attention to the material and learn more. Teaching notes are s 3. in their iPads and are easy to find. Some students spend more time studying now. 'I can listen to my language material or watch teaching videos on the bus, instead of having to wait till I get home.' a student explained. But many adults c 4. that technologies like iPads are doing harm to students. They worry that students might use iPads to download teaching notes and use them to cheat during exams. Some believe that iPads may separate students from each other. If a student spends more time watching videos on an iPad. he will have f 5. chances to have face-to-face communication with others. However, technologies are a 6. _ a part of most students' day-to-day lives. As for cheating, teachers can ask students to hand in their iPads when they take exams. Education needs to make c 87 with the times as technology is playing an important part. We should look forward to a wonderful future when iPads and other technologies can add a lot to the classroom.