The displacement x of a particle varies with time 't' as $x=ae^{-\alpha t}+b e^{\beta t}$ where $a,b,\alpha, \beta$ are positive constants. The velocity of the particle will

Question

$\begin{array}{1 1} (a) go\;on\;decreasing \;with \;time \\(b)be\; independent\; of\; \alpha\;and\; \beta \\(c) drop\;of\;zero\;when\;\alpha=\beta \\(d)\;go\;on\;increasing\;with\;time \end{array}$