(S (S (BASENP (PRP It)) (VP (VP (VBD was) (ADVP (RB previously))) (VP (VBN believed) (SBAR (IN that) (S (NP (QP (RB only) (NN 13)) (BASENP (JJ semi) (NNS trucks))) (VP (VBD were) (VP (VBN involved)))))))) (PERIOD .))