A."abc" B.['a', 'b', 'c'] C.[a, b, c] D.报错
A."gfedcba" B."abc" C."abcde" D."abcdefg"
A.“abc2” B.“abc” C.“abcabc” D.报错
A.a.replace("a", "A") B.a = a.replace("a", "A") C.a.lower() D.a.upper()
A.a.count(a) B.a.count('a') C.a.index('a') D.a.index(a)