$\text{A.}$ $T\left(a_1, a_2, a_3\right)=\left(a_1, a_2+a_3, a_1-a_3\right)$
$\text{B.}$ $T\left(a_1, a_2, a_3\right)=\left(a_1^2, a_2^2, a_3^2\right)$
$\text{C.}$ $T\left(a_1, a_2, a_3\right)=\left(a_1^3, a_2, a_3\right)$
$\text{D.}$ $T\left(a_1, a_2, a_3\right)=\left(a_1, a_1 a_2, a_1+a_2+a_3\right)$
$\text{E.}$
$\text{F.}$