\[\begin{array}{1 1}(1)\overrightarrow{x}=\overrightarrow{0}&(2)\overrightarrow{y}=\overrightarrow{0}\\(3)\overrightarrow{x} and \overrightarrow{y} \;are \;parallel&(4)\overrightarrow{x}=\overrightarrow{0} or\overrightarrow{y}=\overrightarrow{0} or\overrightarrow{x} and \overrightarrow{y} \;are \;parallel\end{array}\]