( ( The ( inner planets ) ) ( ( are ( ( ( ( ( Mercury ( , ( Venus ( , ( Earth , ) ) ) ) ) and ) Mars ) , ) ( which ( are ( close ( to ( the Sun ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ inner) (NNS planets)) (VP (VBP are) (NP (NP (NP (NNP Mercury) (, ,) (NNP Venus) (, ,) (NNP Earth) (, ,)) (CC and) (NP (NNP Mars))) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (ADJP (JJ close) (PP (TO to) (NP (DT the) (NNP Sun))))))))) (. .)))
The inner planets are Mercury, Venus, Earth, and Mars,  which are close to the Sun.
(ROOT (S (NP (NNP Mercury)) (VP (VBZ is) (ADVP (RB always)) (ADJP (ADJP (JJR closer)) (PP (TO to) (NP (DT the) (NN sun)))) (SBAR (IN than) (S (NP (PRP it)) (VP (VBZ is) (PP (TO to) (NP (NN earth))))))) (. .)))
Mercury is always closer to the sun than it is to earth.