PLEASE HELP TRYING TO MAKE HONOR ROLL < PLEASE HELP ME OUT

Which equation has exactly one solution

A. n - 2n + 1 = 2n - 3n - 1
B. 2n - n = 2n - 3n
C. 1 - n - 2n = 1 - 2n - n
D. n - (1 - 2n) = 2n + (n - 1)