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