(S (S (BASENP (DT This)) (VP (MD could) (VP (ADVP (RB possibly)) (VP (VB signal) (SBAR (IN that) (S (BASENP (NNP North) (NNP Korea)) (VP (VBZ is) (VP (VBG preparing) (PP (IN for) (BASENP (DT a) (JJ nuclear) (NNS arms) (NN test))))))))))) (PERIOD .))