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 U.S. officials had no knowledge of the discussions by March.
( ( The ( U.S. officials ) ) ( ( ( had ( ( no knowledge ) ( of ( the discussions ) ) ) ) ( by March ) ) . ) )
(ROOT (S (NP (DT The) (NNP U.S.) (NNS officials)) (VP (VBD had) (NP (NP (DT no) (NN knowledge)) (PP (IN of) (NP (DT the) (NNS discussions)))) (PP (IN by) (NP (NNP March)))) (. .)))