( ( Field theory ) ( ( relates ( forces ( in ( electricity ( , ( ( magnetism and ) gravity ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Field) (NN theory)) (VP (VBZ relates) (NP (NP (NNS forces)) (PP (IN in) (NP (NN electricity) (, ,) (NN magnetism) (CC and) (NN gravity))))) (. .)))
Field theory relates forces in electricity, magnetism and gravity.
(ROOT (S (NP (NNP Gravity) (CC and) (NNP magnetism)) (VP (VBP are) (NP (DT both) (JJ common) (NNS forces))) (. .)))
Gravity and magnetism are both common forces.