如图所示，实线是某电场中的电场线，虚线是一个带负电的粒子仅在电场力作用下的运动轨迹，若带电粒子是从a处运动到b处，以下判断正确的是（   ）

    Here comes the last term of Junior 3. Terrible! The big exam is coming in less than two months. You still have a lot to do. How will you spend it? We invited three students to share their stories.
Dou Yi, 15,Beijing
    My chemistry  used to be poor in the past. I got scores of around 40 on every test. During the last term, I decide to beat chemistry. I will start to work hard. In class I take every possible note. After school, I spend most of my time studying chemistry. My parents also ask their friend, a chemistry teacher, to help me . Finally in the latest exam, I got 65! How happy I am!
Wang Zhaolin, 16, Chongqing
    My foot got hurt a week before the big PE exam . Luckily, I recovered（康复） in time. For PE , all you need is to practice. Sports can also help you relax. Be careful not to get hurt as I did.
Wang Feixuan, 15, Xi'an
    My experience is that for Junior3, every minute of the last term is important. Don't waste any of them. I try to remember English words while waiting in line to get my lunch. I read textbooks on the bus to and from school. I work hard at home and sometimes stay up late studying. Want to have fun? Leave it for the summer holiday after the big exam!

调查六年级300名学生的运动爱好，分布情况如图：

功的两个必要因素：一个是作用在物体上的 ____ ，另一个是物体在力的方向上移动的____   。