如图所示，在竖直向下的匀强磁场中有两根竖直放置的平行粗糙导轨CD、EF，导轨上放有一金属棒MN．现从t=0时刻起，给金属棒通以图示方向的电流且电流强度与时间成正比，即I=kt，其中k为常量，金属棒与导轨始终垂直且接触良好．下列关于金属棒的速度v、加速度a随时间t变化的图象可能正确的是（   ）

用动词的适当形式填空。
⑴In class, every student in our class ____  (take) notes carefully
⑵–Do you think whether the book called Harry Porter is worth ____  (read)?  - Yes, of course.
⑶ I called you yesterday afternoon, but you were out. - Oh, I ____ (watch) a football match on the playground.
⑷ Can you hear the two boys ____  (argue) with each other right now?
⑸The person we talked about ____  (visit) our school next week..

1900年，八国联军发动侵华战争的直接目的是（　　）

分解因式：x²-9+3x（x-3）

是真是假