题目

In Brilain， some people say they will do anything if a famous person they love asks them to．One in three people in Briain have a new kind of disease﹣ ﹣they love a famous person too much．     Some people love famous stars like Britney Spears， David Beckham or even Tony Blair．It is not just the young， grown﹣ups have the same problem． One in four people are so interested in their heroes that it affects their life．     There are two ways of worshipping famous people． One way is just to follow them or talk about them with friends for fun． The other is a more回旋加速器是加速带电粒子的装置，其核心部分是分别与高频交流电源两极相连接的两个D形金属盒，两盒间的狭缝中形成周期性变化的电场，使粒子在通过狭缝时都能得到加速，两D形金属盒处于垂直于盒底的匀强磁场中，如图所示。设D形盒半径为R。若用回旋加速器加速质子时，匀强磁场的磁感应强度为B，高频交流电频率为f。则下列说法正确的是(    )       A．质子被加速后的最大速度不可能超过2πfR B．质子被加速后的最大速度与加速电场的电压大小无关 C．只要R足够大，质子的速度可以被加速到任意值 D．不改变B和f，该回旋加速器也能用于加速α粒子