下面几位文化名人中，对人类文化传播贡献最大的是[ ]
A．张衡
B．蔡伦
C．张仲景
D．华佗
答案：B
在Rt△ABC中，∠C=90゜，AC=5，BC=12，以C为圆心，R为半径作圆与斜边AB相切，则R的值为______．
．______Hard you may try, you can’t possibly persuade Tom to give up smoking, for he is so addicted to it.
A．Whatever
B．However
C．Whichever
D．Whenever
