The set of all values of λ for which the system of linear equations 2x1 - 2x2 + x3 = λx1, 2x1 - 3x2 + 2x3 = λx2 and -x1 + 2x2 = λx3 has a non-trivial solution
(a) is an empty set
(b) is a singleton set
(c) contains two elements
(d) contains more than two elements