免疫系统是抗击癌症的关键。

Freedom is not merely the opportunity to do as one pleases; neither is it merely the opportunity to choose between set alternatives. Freedom is, first of all, the chance to formulate the available choices, to argue over them - and then, the opportunity to choose.

用秤称一称，才能知道轻重；用尺量一量，才能知道长短。