For the following parameterized curve, find the unit tangent vector.

$r(t)=($:$e^{2t},2e^{2t},2e^{9t}$:$),$ for $t0$

Select the correct answer below and, $if$ necessary, fill $in$ the answer boxes within your choice.

$A.T(t)=1,,$

$(Type$ exact answers, using radicals $as$ needed.$)$

$B.$ Since $r^{\text{'}}(t)=0,$ there $isno$ tangent vector.