大佬们看看这儿哪错了

这是错误
D:\Python3.9.2\1\venv\Scripts\python.exe D:/Python3.9.2/1/字典.py
Traceback (most recent call last):
File "D:\Python3.9.2\1\字典.py", line 21, in <module>
q = a[k[i]] + q
KeyError: 'CD'
进程已结束，退出代码 1