11.BD【解析】图甲中粒子做类平抛运动,水平位移和竖直位移大小相等,由=·E?得t=2mA项错误;图乙中粒子做匀速圆周运动,由几何关系知粒子在c点的速度方向竖直向下,B项正确;如果b、c两点重合,则粒子做类平抛运动的水平位移大小与图乙中粒子做匀速圆周运动的半径一定相等,则E有w·=9E=9B,可得B=2,C项错误;粒子从a点到b点所用时间为2m9E,粒子从a点到c点所用时间为1.2xm,又b、c两点重合时有B=20则图甲、乙中粒子运动时间的比值为2,D项正确。

书面表达Dear fellow studentsSpring is coming! It brings us hope as well as a lot of infectious diseases. Some measures are supposed to be taken to protect读 us from the virus如First of all people with cold or flu-like symptoms should wear smasks to prevent viruses spreading from person to person. Ofcourse, don't forget to wash your hands properly before eating orH after using the toilet. Regular exercise is also one of the most im-tt I portant ways to help you stay away from catching any disease. Ifpossible,avoid going to cro wded public places such as cinemas.shopping malls and internet bars etc.A healthy body results from good healthy habits, so let's actogether to fight against diseases and create a better lifelThe Student Union

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