Trying to make honor roll <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)

This is a rational expression because the denominator contains a variable. this is a polynomial with 3 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 4 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 4 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 3 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 5 terms.