( ( ( Semi-submersible ( drilling rigs ) ) ( which ( ( ( ( are ( moored ( to ( the ( ocean bottom ) ) ) ) ) , ) but ) ( have ( some ( propulsion capability ) ) ) ) ) ) ( , ( ( ( are also ) ( considered ( marine vessels ) ) ) . ) ) )
(ROOT (S (NP (NP (JJ Semi-submersible) (NN drilling) (NNS rigs)) (SBAR (WHNP (WDT which)) (S (VP (VP (VBP are) (VP (VBN moored) (PP (TO to) (NP (DT the) (NN ocean) (NN bottom))))) (, ,) (CC but) (VP (VBP have) (NP (DT some) (NN propulsion) (NN capability))))))) (, ,) (VP (VBP are) (ADVP (RB also)) (VP (VBN considered) (NP (JJ marine) (NNS vessels)))) (. .)))
Semi-submersible drilling rigs which are moored to the ocean bottom, but have some propulsion capability, are also considered marine vessels.
(ROOT (S (NP (NNS Scientists)) (VP (VBP know) (SBAR (IN that) (S (NP (DT some) (NNS mountains)) (VP (VBD were) (ADVP (RB once)) (PP (IN at) (NP (NP (DT the) (NN bottom)) (PP (IN of) (NP (DT an) (NN ocean))))) (SBAR (IN because) (S (NP (JJ marine) (NNS fossils)) (VP (VBP have) (VP (VBN been) (VP (VBN found) (PP (IN on) (NP (NP (DT the) (NNS peaks)) (PP (IN of) (NP (DT some) (NNS mountains)))))))))))))) (. .)))