$\begin {array} {1 1} (a)\;the\: same\: direction,\: but\: differ\: in\: phase \: by \: 90^{\circ} \\ (b)\;the\: same\: direction\: and\: are\: in \: phase \\ (c)\;mutually\: perpendicular\: direction\: and \: are \: in\: phase \\ (d)\;none\: of \: these \end {array}$
