back and forth 来来回回的;

　　flesh and blood 血肉之躯;

　　heavy and light 轻重;

　　iron and steel 钢铁;

　　night and day 夜以继日的;

　　off and on 断断续续的;

　　old and young 无论老少;

　　one and only 唯一;

　　rain or shine 不论阴晴;

　　twos and threes 三三两两