mystery: applies to what cannot be fully understood by human reason or less strictly to whatever resists or defies explanation: the ~ of the stone monoliths on Easter Island.   单块巨石，独石柱       复活节岛


problem: applies to any question or difficulty calling for a solution or causing concern: the ~s created by high technology.


enigma: applies to an utterance or behavior that is difficult to interpret: his suicide was an ~ his family never understood.


riddle: suggests an enigma or problem involving paradox or apparent contradiction: the ~ of the reclusive billionaire.


puzzle: applies to an enigma or problem involving paradox or apparent contradiction that challenges ingenuity for its solution: the mechanisms of heredity were long a ~ for scientists.    (ingenious聪敏suggests brilliance or cleverness in inventing or discovering能够聪明地发明发现，如an ingenious computer engineer一个聪敏的电脑工程师)


conundrum: applies to a riddle or puzzle whose answer involves a pun or less often to a problem whose solution can only be speculative: posed ~s to which there are no practical solutions.   （pun双关语，用一个词表示多种含义，如the only thing we have to fear is fear丘吉尔:我们唯一需要畏惧的是胆怯，用了fear的两个意思；如why is a river rich? because it has two banks是一道脑筋急转弯，bank河岸或银行；如we must all hang together or we shall all hang separately我们必须团结起来，否则会被一个个吊死，是对hang的双关，分别表示团结一致和吊死）


mystery神秘: 指无法通过推理来理解解释的，problem问题: 泛指需要关注解决的问题困难，enigma迷: 指难以解释的言行，riddle迷:指自相矛盾的迷或问题，puzzle难题: 同上，挑战人的聪敏，conundrum无解难题: 指答案带有双关，只能猜测无法解决的迷或难题


记忆方法: 1）首字母MPERPC想成ME Plus PRC我和中国<==神秘

         2）神秘的意思是令人困惑的mean something which baffles or perplexes.    (perplex表示困惑时比baffle程度重，baffle仅表示疑惑不解to confuse, puzzle，但perplex到了让人worry担心的地步，如an odd change of personality that perplexes her friends她性格突变，令朋友十分困惑.，有词典把perplex解释为十分困惑to feel completely baffled，又如he perplexed me with this problem他用这个问题难住了我)