The set of all values of $\lambda$ for which the system of linear equations:\\
$2 x _ { 1 } - 2 x _ { 2 } + x _ { 3 } = \lambda x _ { 1 }$\\
$2 x _ { 1 } - 3 x _ { 2 } + 2 x _ { 3 } = \lambda x _ { 2 }$\\
$- x _ { 1 } + 2 x _ { 2 } = \lambda x _ { 3 }$\\
has a non-trivial solution,\\
(1) Contains more than two elements.\\
(2) Is an empty set.\\
(3) Is a singleton.\\
(4) Contains two elements.