通货膨胀的老大难问题仍然困扰着他们.

The old bugaboo of inflation still bothers them.

首先，从汉语语言学研究的角度看，词类问题也一直是一个老大难问题。

On the one hand, POS study is always a Gordian knot to Chinese linguists ever since the beginning of Modern Chinese Linguistics.