( ( Plane mirrors ) ( ( are ( ( ( the ( only type ) ) ( of mirror ) ) ( ( for which ) ( ( a ( real object ) ) ( ( ( ( ( always ( produces ( ( an image ) ( that ( is virtual ) ) ) ) ) , ) erect ) and ) ( ( of ( the ( same size ) ) ) ( as ( the object ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Plane) (NNS mirrors)) (VP (VBP are) (NP (NP (DT the) (JJ only) (NN type)) (PP (IN of) (NP (NN mirror))) (SBAR (WHPP (IN for) (WHNP (WDT which))) (S (NP (DT a) (JJ real) (NN object)) (VP (VP (ADVP (RB always)) (VBZ produces) (NP (NP (DT an) (NN image)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADJP (JJ virtual))))))) (, ,) (VP (VB erect)) (CC and) (VP (PP (IN of) (NP (DT the) (JJ same) (NN size))) (PP (IN as) (NP (DT the) (NN object))))))))) (. .)))
Plane mirrors are the only type of mirror for which a real object always produces an image that is virtual, erect and of the same size as the object.
(ROOT (S (NP (DT A) (NN plane) (NN mirror)) (VP (VP (VBZ has) (NP (DT a) (ADJP (JJ flat) (JJ reflective)) (NN surface))) (CC and) (VP (VBZ forms) (NP (RB only) (JJ virtual) (NNS images)))) (. .)))