Answer:
(C) (x+1) is not a factor
Explanation:
To show that x+1 is not a factor, in other words to show that the polynomial cannot be written as a product

it suffices to test that x=-1 is not a root of the original cubic:

which is hereby shown and the option (A) is out.
Option (B) is non-sense.
Option (C) is the correct answer.