Hi mike.
Here is my question

While(a) working as a labour union minister from(b) 1970 to(c) 1980, Mr. X fought(d) to ensure the rights of the labours. No error(e).

Is there any error in the sentence?
I did (a) because I thought while was inappropriate and when was correct.
So,what do you think?

There’s no error with “while.”