To signal an emergency, use the rule of three; 3 shouts, 3 horn blasts, or 3 whistles.
The world is a fine place and worth fighting for.
墨翟我上没有侍奉国君的差事,下没有耕田种地的艰难,我怎么敢放弃读书呢?
数学的本质在于它的自由。