题目

某Python程序代码如下： s='t1Hr2a3' s1='' ; s2=''; i = 0 while i < len(s):     if '0'<=s[i]<='9':          s1 = s1 + s[i]      elif 'a'<=s[i]<='z':         s2 = s[i] + s2          i = i + 1         ans = s2 + s1 print(ans) 程序执行后，输出的结果是(      ) A . 12art3 B . art123 C . rta123 D . art321 答案：B

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