问题描述：
17.My sister _____ a letter when I got home last night.
17.My sister ______ a letter when I got home last night.A.is writing B.was writing C.wrote D.is reading 我选的B 为什么
17.My sister ______ a letter when I got home last night.A.is writing B.was writing C.wrote D.is reading 我选的B 为什么
问题解答：
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