The procedures(程序) of operating a computer have been ______ several times, the results

of which have made it much easier _______.   [ ]

A. cut down; to operate              

B. simplified; to be operated  

C. reduced; to be operated            

D. simplified; to operate

下图所示的四幅图中，分别标出了磁场方向、带正电粒子的运动方向和其所受洛伦兹力的方向，其中正确标明了带电粒子所受洛伦兹力F方向的是