大学英语：重要词汇be on duty 值班，值日，在上班时

212.be in duty bound to(do)(=be required by one's job or esp.by conscience)有义务(做)

213.be eager for 想得到，盼望

214.by ear(=play music from memory without having seen it printed)凭记忆，不看乐谱

215.have an ear for(=have keen recognition of sounds esp.in music and language)对...有鉴赏力

216.a word in one's ear 私房话，秘密话

217.on earth 究竟，到底，全然

218.with ease(=easily)容易，不费力