题目

 Going green seems to be fad（时尚）for a lot of people these days. Whether that is good or bad, we can’t really say, but for the two of us, going green is not a fad but a lifestyle. On April 22, 2011, we decided to go green every single day for an entire year. This meant doing 365 different green things, and it also meant challenging ourselves to go green beyond easy things. Rather than recycle and reduce our energy, we had to think of 365 different green things to do and this was no easy task. With the idea of going green every single day for a year, Our Green Year started. My C919大型客机是我国具有自主知识产权的大型喷气式民用飞机。如果客机绕地球做匀速圆周运动，空气阻力大小不变，不考虑油料消耗导致客机质量变化。关于客机，下列说法正确的是A. 处于平衡状态 B. 速度变化率为零C. 发动机的功率不变 D. 向心力完全由地球引力提供