( ( An ( important need ) ) ( is ( to ( identify ( ( ( ( ( ( the ( viral host ) ) , ) and ) ( exogenous factors ) ) and ) ( ( their interactions ) ( that ( determine ( ( the ( natural history ) ) ( of ( hepatitis C. ) ) ) ) ) ) ) ) ) ) )
(ROOT (S (NP (DT An) (JJ important) (NN need)) (VP (VBZ is) (S (VP (TO to) (VP (VB identify) (NP (NP (NP (DT the) (JJ viral) (NN host)) (, ,) (CC and) (NP (JJ exogenous) (NNS factors))) (CC and) (NP (NP (PRP$ their) (NNS interactions)) (SBAR (WHNP (WDT that)) (S (VP (VBP determine) (NP (NP (DT the) (JJ natural) (NN history)) (PP (IN of) (NP (NNP hepatitis) (NNP C.)))))))))))))))
An important need is to identify the viral host, and exogenous factors and their interactions that determine the natural history of hepatitis C.
(ROOT (S (NP (NNP Community) (NNS interactions)) (VP (VBP are) (NP (NP (JJ important) (NNS factors)) (PP (IN in) (NP (JJ natural) (NN selection))))) (. .)))