问题描述：
这题：过去分词作状语的选择题
Before ______ white,the door should be cleaned thoroughly.
A painted
B being painted
C having been painted
为什么?每个选项都说明一下,
Before ______ white,the door should be cleaned thoroughly.
A painted
B being painted
C having been painted
为什么?每个选项都说明一下,
问题解答：
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