题干
Chinese President Xi Jinping, _________by Manchester United former players and ambassadors, enjoyed an exhibition from National Football Museum, ________ major historical artifacts(文物)were on display.
A：greeting; where
B：greeting; in which
C：greeted; where
D：greeted; in that
答案(点此获取答案解析）
C
和
粒子氦核42He以相同的速率在同一匀强磁场中做匀速圆周运动，轨道半径分别为
和
，周期分别为
和
，则下列选项正确的是（ ）。