( ( The ( simplest hydrocarbon ) ) ( ( is ( ( one atom ) ( of ( carbon ( linked ( to ( ( four atoms ) ( of hydrogen ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJS simplest) (NN hydrocarbon)) (VP (VBZ is) (NP (NP (CD one) (NN atom)) (PP (IN of) (NP (NP (NN carbon)) (VP (VBN linked) (PP (TO to) (NP (NP (CD four) (NNS atoms)) (PP (IN of) (NP (NN hydrogen)))))))))) (. .)))
The  simplest hydrocarbon is one atom of carbon linked to four atoms of hydrogen.
(ROOT (S (NP (NNS Hydrocarbons)) (VP (VBP are) (VP (VBN made) (PP (IN of) (NP (NP (CD one) (NN carbon)) (CC and) (NP (CD four) (NN hydrogen) (NNS atoms)))))) (. .)))
Hydrocarbons are made of one carbon and four hydrogen atoms.