题目

Hi, I'm Amanda! I was asked to share more about my experience as an online student of Virtual High School to give you a better idea of what it's like, or at least what it was like for me. Usually I was working on four courses at a time, just as if I were in a brick-and-mortar high school. But unlike students in a brick-and-mortar school, I did not work for a set amount of time each day. Sometimes I would spend the whole day on English, and on another I would study among all four, depending on how focused I was or what I felt motivated to do. I loved skating during my high school years, both as 火车拐弯时，需要向心力作用，对于向心力的分析，正确的是 A．由于火车本身作用而产生向心力 B．主要由于内外轨的高度差使车身略有倾斜，车身所受重力的分力产生了向心力 C．火车在拐弯时的速率小于规定速率时，内轨将给火车侧压力，侧压力就是向心力 D．火车拐弯时的速率大于规定速率时，外轨将给火车侧压力，侧压力成为火车转弯的向心力的一部分