红花词：though although while for example for instance because however
绿叶：since when if only only if if
考研完型有什么红花绿叶原则,谁能告诉我下有哪些是“红花词”（必选词）“绿叶词”（必不选词）,
红花词：though although while for example for instance because however
绿叶：since when if only only if if