Keesha was asked to use the remainder theorem to determine whether x+1 is a factor of the function f(x)=x^3+2x^2-5x-6 . which statement can be determined to be true using keesha's results?

a. 1 is a zero of the function because the remainder is zero.

b. 1 is a zero of the function because it is the coefficient of the first
term.

c. –1 is a zero of the function because the remainder is zero.

d. –1 is a zero of the function because it is a factor of the last term.