( Estonia ( ( is ( ( the ( only country ) ) ( in ( ( the world ) ( that ( ( uses ( oil shale ) ) ( as ( its ( primary ( energy source ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Estonia)) (VP (VBZ is) (NP (NP (DT the) (JJ only) (NN country)) (PP (IN in) (NP (NP (DT the) (NN world)) (SBAR (WHNP (WDT that)) (S (VP (VBZ uses) (NP (NN oil) (NN shale)) (PP (IN as) (NP (PRP$ its) (JJ primary) (NN energy) (NN source)))))))))) (. .)))
Estonia is the only country in the world that uses oil shale as its primary energy source.
(ROOT (S (NP (NNP Oil)) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (RB commonly) (VBN used)) (NN source)) (PP (IN of) (NP (NP (NN energy)) (PP (IN in) (NP (DT the) (NN world))))))) (. .)))