when necessary做时间状语时,如何解释
\u6c42\u89e3\u91ca\uff0c\u5173\u4e8ewhen\u7684\u65f6\u95f4\u72b6\u8bed\u4ece\u53e5\u7684\u4e00\u9053\u9898when choosing\u548cwhen you choose\u90fd\u5bf9\uff0c\u5728\u8fd9\u53e5\u4e2dwhen choosing=when you choose\uff0c\u662f\u4e0d\u662f\u4f60\u628a\u54ea\u4e2a\u7b54\u6848\u4e2d\u7684\u5355\u8bcd\u6253\u5dee\u4e86\u3002
\u4ed4\u7ec6\u770b\u770bwhen choosing\u548cwhen you choose\u4e2d\u54ea\u4e2a\u5355\u8bcd\u6253\u5dee\u4e86\u3002
when\u5728\u8fd9\u91cc\u4f5c\u4e3a\u201c\u8fd9\u65f6\u5019\u201d\u8bb2
\u3000\u3000\u82f1\u8bed\u4e2d\uff0c\u8fde\u8bcdwhen\u8868\u793a"\u5f53\u2026\u2026\u65f6\u5019"\uff0c\u5f15\u5bfc\u7684\u65f6\u95f4\u72b6\u8bed\u4ece\u53e5\u8868\u793a\u4e0e\u4e3b\u53e5\u52a8\u4f5c\u540c\u65f6\u6216\u4e0d\u540c\u65f6\uff0c\u4ece\u53e5\u52a8\u8bcd\u7528\u5ef6\u7eed\u6216\u975e\u5ef6\u7eed\u6027\u90fd\u53ef\u4ee5\u3002\u5982\uff1a
\u3000\u3000I'll telephone you when I get there tomorrow.\u660e\u5929\u6211\u5230\u90a3\u91cc\u7684\u65f6\u5019\u5c31\u7ed9\u4f60\u6253\u7535\u8bdd\u3002
\u3000\u3000\u4f46\u662f\u5728\u9ad8\u4e00\u65b0\u6559\u6750Unit 15 "The necklace"\u4e2d\uff0c\u5c31\u51fa\u73b0\u4e86when\u7528\u4f5c\u5e76\u5217\u8fde\u8bcd\uff0c\u8868\u793a"\u5c31\u5728\u8fd9\u65f6"(=and this time/just at that time)\u7684\u7528\u6cd5\u3002\u5982\uff1a
\u3000\u3000Tom was sitting near the fire when he heard a knock at the door.\u6c64\u59c6\u6b63\u5750\u5728\u706b\u7089\u8fb9\uff0c\u8fd9\u65f6\u4ed6\u542c\u5230\u4e00\u9635\u6572\u95e8\u58f0\u3002
\u3000\u3000I was just going to speak when the doorbell rang.\u6211\u6b63\u51c6\u5907\u8bb2\u8bdd\uff0c\u8fd9\u65f6\u95e8\u94c3\u54cd\u4e86\u3002
\u3000\u3000\u5f53\u5e76\u5217\u8fde\u8bcdwhen\u7528\u4e8e"\u5c31\u5728\u8fd9\u65f6\uff0c\u6b63\u5728\u8fd9\u65f6"\u7684\u7528\u6cd5\u65f6\uff0c\u5b83\u6240\u5f15\u5bfc\u7684\u5e76\u5217\u53e5\u8868\u793a\u52a8\u4f5c\u53d1\u751f\u540e\uff0c\u53e6\u4e00\u4e2a\u5e76\u5217\u53e5\u6240\u8868\u793a\u7684\u52a8\u4f5c\u4e4b\u540e\uff0c\u4e00\u822c\u4e0d\u53ef\u4ee5\u7528\u5176\u4ed6\u8bcd\u4ee3\u66ff\uff0c\u5e38\u7528\u4e8e\u4ee5\u4e0b\u7ed3\u6784\uff1a
\u3000\u30001.was/were doing +when\u610f\u601d\u4e3a"\u5c31\u5728\u8fd9\u65f6\uff0c\u6b63\u5728\u8fd9\u65f6"\u3002\u5982\uff1a
\u3000\u3000I was walking in the street when someone called me from behind.\u6211\u6b63\u5728\u8857\u4e0a\u8d70\uff0c\u5c31\u5728\u8fd9\u65f6\u6709\u4eba\u4ece\u540e\u9762\u53eb\u6211\u3002
\u3000\u3000They were discussing the problem when the teacher came in.\u4ed6\u4eec\u6b63\u5728\u8ba8\u8bba\u95ee\u9898\uff0c\u5c31\u5728\u8fd9\u65f6\u8001\u5e08\u8fdb\u6765\u4e86\u3002
\u3000\u30002.was/were about to do...when\u610f\u601d\u4e3a"\u6b63\u8981/\u6b63\u51c6\u5907\u505a\u67d0\u4e8b\uff0c\u5c31\u5728\u8fd9\u65f6\u2026\u2026"\u3002\u5982\uff1a
\u3000\u3000She was about to go out when an unexpected visitor came.\u5979\u6b63\u51c6\u5907\u51fa\u53bb\uff0c\u8fd9\u65f6\u6765\u4e86\u4e00\u4f4d\u4e0d\u901f\u4e4b\u5ba2\u3002
\u3000\u3000We were about to set out when it began to rain.\u6211\u4eec\u6b63\u8981\u52a8\u8eab\uff0c\u5c31\u5728\u8fd9\u65f6\u5f00\u59cb\u4e0b\u96e8\u4e86\u3002
\u3000\u30003.be+\u8868\u793a\u72b6\u6001\u7684\u4ecb\u8bcd\u77ed\u8bed+when\u610f\u601d\u4e3a"\u6b63\u5728\u505a\u67d0\u4e8b\uff0c\u5c31\u5728\u8fd9\u65f6\u2026\u2026"\u3002\u5982\uff1a
\u3000\u3000They were at work in the office that
\u3000\u3000afternoon when a big fire broke out.\u90a3\u5929\u4e0b\u5348\u4ed6\u4eec\u6b63\u5728\u529e\u516c\u5ba4\u5de5\u4f5c\uff0c\u5c31\u5728\u8fd9\u65f6\u4e00\u573a\u5927\u706b\u53d1\u751f\u4e86\u3002
\u3000\u3000We were on duty in the classroom when a boy rushed in.\u6211\u4eec\u6b63\u5728\u6559\u5ba4\u91cc\u503c\u65e5\uff0c\u5c31\u5728\u8fd9\u65f6\u4e00\u540d\u7537\u5b69\u51b2\u4e86\u8fdb\u6765\u3002
\u3000\u3000Li Ping was on his way home when two boys stopped him.\u674e\u5e73\u6b63\u5f80\u5bb6\u8d70\uff0c\u7a81\u7136\u4e24\u4e2a\u7537\u5b69\u62e6\u4f4f\u4e86\u4ed6\u3002
\u3000\u3000\u6ce8\u610f\uff1a\u5728\u4e0a\u8ff0\u4e09\u79cd\u7528\u6cd5\u7684\u7ed3\u6784\u4e2d\uff0cwhen\u5f15\u5bfc\u7684\u53e5\u5b50\u4e0d\u80fd\u653e\u5728\u53e5\u9996\u3002
\uff08\u6458\u81ea\u82f1\u8bed\u8f85\u5bfc\u62a5\uff09
可以改为Try to turn to the dictionary when you need it.need及物，要接宾语的。
又例如：
Help is always at hand when you need it.=Help is always at hand when neccesary.
扩展阅读：have anything to do with ... be taken when necessary ... go back a long way ... benefit from ... necessary top off the ... in handy some day ... phone me when necessary ... for external use ... bring out the best ...
