Meaning:

老大难 (lǎo dà’nán) nagging problems

Usage:

“老大难”是指复杂的，难以解决或者是很长时间都没有进展的事情。

“老大难” means matters are difficult or taking a long time to deal with.

Examples:

1. 她年龄越来越大，还很挑剔，找对象成了老大难了。

    Tā niánlíng yuè lái yuè dà, hái hĕn tiāotì, zhǎo duìxiàng chéng le lǎo dà’nán le

    As she is not young and nit-picking, now finding a boyfriend becomes a nagging problem.

2. 这个班的学生很调皮，成绩差，是全校有名的老大难班级。

    Zhè ge bān de xuésheng hĕn tiáopí, chéngjì chà, shì quánxiào yǒumíng de lǎo dà’nán bānjí

    The students in this class are very naughty and have poor grades. It is a problem in the school.