单项选择题
设语言L={w|w∈{a,b}
+
且w中a和b的个数相等},产生语言L的上下文无关文法是(28)。
A.G
a
=(V
T
={a,b},V
N
={S,A,B},S,P),其中P为, S→a|aA|bSS A→aB|bS B→b|bA|aBB
B.G
b
=(V
T
={a,b},V
N
={S,A,B},S,P),其中P为, S→b|bB|aSS B→aS|bA A→a|aB|bAA
C.G
c
=(V
T
={a,b},V
N
{S,A,B},S,P),其中P为, S→aB|bA A→a|aS|bAA B→b|bS|aBB
D.G
d
=(V
T
={a,b},V
N
={S,A,B},S,P),其中P为, S→aB|bA|s A→aS|bAA B→bS|aBB