这是一个非常困难的问题。

This is too difficult a problem.

youdao

高速公路交通流模型是一个高阶非线性时变系统，这使得该模型的辨识问题成为一个非常困难的问题。

The macro model of traffic flow in freeway is a high order, nonlinear and time variant system which makes the problem of its identification become very difficult.

youdao

他补充说：“在任何实用的能量转换的人工光合系统中这都是一个非常困难的问题，现在它已经被解决了。”

He adds: "There is a daunting combination of problems to be solved before this or any other artificial photosynthetic system could actually be useful for energy conversion."

youdao