For $t0,$ the position of a particle moving along the $x-$axis is given by $x(t)=sint-cost.$ What is the acceleration of the particle at the point where the velocity is first equal to $0?$

$($A$)-\sqrt[\phantom{2}]{2}$

$($B$)-1$

$($C$)0$

$($D$)1$

$($E$)\sqrt[\phantom{2}]{2}$