(S (S (S (VP (VBN Watched) (PP (IN by) (NP (BASENP (NNS thousands)) (PP (IN of) (NP (BASENP (NNS students)) (VP (VBN gathered) (ADVP (RB outside))))))))) (COMMA ,) (S (BASENP (DT a) (NN fire) (NN extinguisher)) (VP (VP (VBD was) (VP (VBN thrown) (PP (IN from) (BASENP (DT the) (NN roof))))) (COMMA ,) (S (VP (VP (VBG giving) (BASENP (JJ glancing) (NNS blows))) (PP (TO to) (NP (BASENP (NN two) (NN police) (NNS officers)) (PP (IN on) (NP (BASENP (DT the) (NN ground)) (ADVP (NP (BASENP (NN 70) (NNS feet)) (PRN (LRB -LRB-) (BASENP (NN 21) (NNS metres)) (RRB -RRB-))) (RB below))))))))))) (PERIOD .))