211．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

219．at (one's) ease ( = without worry or nervousness) 自在，不拘束

220．put sb. at his / her ease (=free sb. from worry or nervousness) 使某人感到无拘束

221．economize¹ on (=save sth. instead of being wasteful) 节省

222．have an effect on 对……有影响

223．be in effect (=be in operation) 有效

224．go into effect 生效。(近：come into effect; take effect; be brought into effect)

225．in effect (=in fact, really) 实际上