The curve given by the parametric equations

$x=t^3-3t$ and $y=t^2$

is

a$.$ concave down when $t<mn>0</mn>$

b$.$ concave down when $t>0t>1-1\frac{-1}{2}$

$c.$ concave $up$ when $t>0$

$d.$ concave $up$ when $t>1$

$e.$ concave $up$ when $-1$