答:一1. S -> aS | ε 2. S -> aS | Sb | ab二设 有字符串序列 abc, 而字符串 abc 符合是文法S.abc 有两种推导 ① S -> Ac, A -> bc ② S -> aB, B -> bc有两语法树,二义文法三不好意思忘记了短语、直接短语和句柄课本上应该有
