They so was because no Plus back .
(ROOT_0 (S_0 (ATS_3 (ATS_1 (NP_1 (PRP_0 They)) (ADVP_0 (RB_0 so))) (VP_3 (ATVP_1 (VP_5 (VBD_1 was) (ADVP_0 (IN_2 because) (RB_1 no))) (CC_0 Plus)) (ADJP_0 (RP_0 back)))) (DOT_0 .)))