The impulse response h(t) of a linear time invariant continuous time system is described by h(t) = exp(αt)u(t) + exp(βt)u(-t) where u(-t) denotes the unit step function, and α and β are real constants. This system is stable if

A. α is positive and β is positive

B. α is negative and β is positive

C. α is negative and β is negative

D. α is positive and β is negative

Answer: Option B