一定要长期坚持，当遇到内心难以解决的困惑时，可以翻看之前的记录，寻找相似的状态，看看当时的自己是如何克服的。
Must insist for a long time, when the heart is difficult to solve the puzzle, can look at the previous record, looking for a similar state, look at how they are overcome.
在化学工业和能源生产中，结垢是一个长期存在而又难以解决的实际问题。
In chemical industry and energy production, scale is a long-standing and actual difficult problem.
这两本书都解决了史学家和姓氏学家长期迷惘而难以解决的一些问题。
Both the two books have solved some of the problems that puzzled historians and surname experts for a long time.
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