"老大难" (lǎo dà nán) means a knotty problem, which is complicated and difficult to resolve. It may take a long time, but finally goes nowhere.
rén men wǎng wǎng yǐ wéi bù ān quán de zhù shè zuò fǎ shì yí ge lǎo dà nán wèn tí, bù róng yì jiě jué.
Unsafe injection practices are often viewed as a chronic problem with no easy solution.
zhè ge bān zhì xù luàn, chéng jì chà, shì quán xiào yǒu míng de lǎo dà nán bān jí.
The class is notorious for its disorder and poor performance. It's a well-known outstanding problem of the school.
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