However, despite exhaustive research, I am reluctantly forced to resort to the familiar lexical locution, `Source unknown.
( However ( , ( ( despite ( exhaustive research ) ) ( , ( I ( ( ( am reluctantly ) ( forced ( to ( ( ( ( resort ( to ( the ( ( familiar lexical ) locution ) ) ) ) , ) ` ) ( Source unknown ) ) ) ) ) . ) ) ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (PP (IN despite) (NP (JJ exhaustive) (NN research))) (, ,) (NP (PRP I)) (VP (VBP am) (ADVP (RB reluctantly)) (VP (VBN forced) (S (VP (TO to) (VP (VB resort) (PP (TO to) (NP (DT the) (ADJP (JJ familiar) (JJ lexical)) (NN locution))) (, ,) (`` `) (NP (NN Source) (NN unknown))))))) (. .)))
I have done a lot of research, but still cannot find the source.
( I ( ( ( ( ( have ( done ( ( a lot ) ( of research ) ) ) ) , ) but ) ( still ( ( can not ) ( find ( the source ) ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VP (VBP have) (VP (VBN done) (NP (NP (DT a) (NN lot)) (PP (IN of) (NP (NN research)))))) (, ,) (CC but) (VP (ADVP (RB still)) (MD can) (RB not) (VP (VB find) (NP (DT the) (NN source))))) (. .)))