(S (S (ADVP (BASENP (NN Four) (NNS months)) (RB ago)) (COMMA ,) (S (NP (BASENP (DT the) (NNP United) (NNPS States)) (PP (IN with) (NP (BASENP (DT some)) (PP (IN of) (BASENP (PRPD its) (NNS allies)))))) (VP (ADVP (RB also)) (VP (VP (VBD conducted) (NP (BASENP (DT a) (NN series)) (PP (IN of) (NP (BASENP (NNS exercises)) (CC and) (BASENP (JJ naval) (NNS drills)))))) (COMMA ,) (S (ADJP (JJ concerned) (PP (IN with) (S (VP (VBG keeping) (S (BASENP (DT the) (NN strait)) (ADJP (JJ open)))))))))))) (PERIOD .))