Answer
C can be less or equal to A+B but not greater than A+B.IF
Work Step by Step
If $\vec A $ and $ \vec B$ are coaxial then C can be equal to A+B. As the magnitude of sum of two vectors is equal to $\sqrt {A^2 + B^2 +2ABcos\theta }$ so there is no possibility of having C >A+B because maximum value for$ cos\theta$ is 1.
