lǎo dà nán形容问题错综复杂，难于解决：～单位|～问题|这个班秩序乱，成绩差，是全校有名的～班级。
暴雨引起的山体滑坡一直是个难以解决的老大难问题。
这已经是好些年来的老大难问题，但是依然十分难去追踪它。
It has been the big thing for a few years now, but it's extremely hard to track.
人们往往以为不安全的注射做法是一个老大难问题，不容易解决。
Unsafe injection practices are often viewed as a chronic problem with no easy solution.
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