U.S. officials became aware of these secret discussions, certainly by March.
( ( U.S. officials ) ( ( ( ( ( became aware ) ( of ( these ( secret discussions ) ) ) ) , ) ( certainly ( by March ) ) ) . ) )
(ROOT (S (NP (NNP U.S.) (NNS officials)) (VP (VBD became) (ADJP (JJ aware)) (PP (IN of) (NP (DT these) (JJ secret) (NNS discussions))) (, ,) (ADVP (RB certainly) (PP (IN by) (NP (NNP March))))) (. .)))
The officials in the U.S. knew of the discussions by March.
( ( ( The officials ) ( in ( the U.S. ) ) ) ( ( ( knew ( of ( the discussions ) ) ) ( by March ) ) . ) )
(ROOT (S (NP (NP (DT The) (NNS officials)) (PP (IN in) (NP (DT the) (NNP U.S.)))) (VP (VBD knew) (PP (IN of) (NP (DT the) (NNS discussions))) (PP (IN by) (NP (NNP March)))) (. .)))