gather: the most general term, is usually neutral in connotation or may suggest plucking and culling or harvesting: a crowd ~s whenever there is excitement.  (cull采集诗文poetic/literary works或花果to pick poems, literary works, flowers or fruits, 如fresh culled daffodils刚刚采下的水仙花，还表示剔除的劣质，多余的家畜an inferior or surplus livestock animal selected for killing，如a cull cow被剔除的母牛)


collect: often implies careful selection or orderly arrangement with a definite end in view: ~ed books on gardening.


assemble: implies an orderly union or organization of persons or things and a conscious or definite end for their coming or being brought together: the country's leading experts on aeronautics ~d under one roof.


congregate: implies a spontaneous flocking together into a crowd or huddle, usually of similar types: persons were forbidden to ~ under martial law.  flock羊群或鸟群，如flocks and herds羊群和牛群


gather采集: 泛指采集，或表示采摘收割，collect收集: 指采集时仔细挑选安排，有明确目的，assemble召集召开汇编: 表示将人事组织起来，有明确意识目的，congregate聚集集会: 表示自发地聚合成群，通常是同类


记忆方法:  1）首字母GCAC想成唱唱歌啊<==聚集

          2）聚集的意思是使到一起mean to come or bring together into a group, mass, or unit.