From a point $$P(\lambda, \lambda, \lambda)$$ perpendiculars PQ and PR are drawn respectively on the lines y = x, z = 1 and y = -x, z = -1. If P is such that $$\angle QPR$$ is a right angle, then the possible value(s) of $$\lambda$$ is(are)

A

$$\sqrt 2$$

B

$$1$$

C

$$-1$$

D

$$-\sqrt 2$$