$\eqalign{ & a)\,\,d:\left\{ \matrix{ x = 2 + t \hfill \cr  y = 3 - t \hfill \cr  z = 1 \hfill \cr} \right. \cr }$

$\eqalign{& b)\,\,d:\left\{ \matrix{ x = 1+2t \hfill \cr  y = 1 - t \hfill \cr  z = 1 - t \hfill \cr} \right. \cr }$

$\eqalign{& c)\,\,d:\left\{ \matrix{ x = 1 + 5t \hfill \cr  y = 1 - 4t \hfill \cr  z = 1 + 3t \hfill \cr} \right. \cr}$