(S (S (BASENP (NNS Experts)) (VP (VBP say) (SBAR (S (BASENP (DT the) (NNS tubes)) (VP (MD may) (VP (VB have) (VP (VP (VBN become) (ADJP (JJ iced) (RB over))) (COMMA ,) (S (VP (VBG causing) (BASENP (DT the) (NN crash))))))))))) (PERIOD .))