A particle moves along X-axis in such a way that its $x$ -coordinate varies with time $t$ according to the relation $x=2-5 t$ $+6 \mathrm{t}^{2}$. The initial velocity $($ at $\mathrm{t}=0)$ of the particle is
(a) $-5$ unit
(b) 3 unit
(c) 6 unit
(d) $-6$ unit