Can you complete this English expression? It means “a problem that is difficult to solve”.

A hard nut to …..

a) crack

b) squash

c) return

d) crunch

The answer is below!

Answer: a) crack

A hard nut to crack!

Example: This maths problem is a hard nut to crack. I don’t think I can do it.

By I Talk You Talk Press – Easy English Reading