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
