题目

—Volunteering is becoming      popular in China . —Yeah, people are now aware that helping others is helping themselves. A. naturally         B. successfully       C. splendidly       D. increasingly 答案：D 解析: 略4．宇宙飞船（内有宇航员）绕地球做匀速圆周运动，地球的质量为M，宇宙飞船的质量为m，宇宙飞船到地球球心的距离为r，引力常量为G，宇宙飞船受到地球对它的万有引力F=$\frac{GMm}{{r}^{2}}$；飞船内的宇航员处于失重状态（填“超重”或“失重”），宇航员随身携带的天平不能正常使用（填“能”或者“不能”）．