If `G` is the set of all matrices of the form `[xxxx]` , where `x in R-{0}` , then the identity element with respect to the multiplication of matrices as binary operation, is `[1 1 1 1]` (b) `[-1//2-1//2-1//2-1//2]` (c) `[1//2 1//2 1//2 1//2]` (d) `[-1-1-1-1]`