I used to school mountains , <apostrophe><apostrophe>
(ROOT_0 (S_0 (ATS_2 (SBAR_0 (S_1 (NP_0 (PRP_1 I)) (VP_5 (VBD_2 used) (PP_2 (TO_0 to) (NP_3 (NN_0 school) (NNS_1 mountains)))))) (COMMA_0 ,)) (APOSTROPHE_0 <apostrophe><apostrophe>)))