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题目内容
（国家开放大学开放英语）
Silk __________ by Chinese for thousands of years now.
单选题 (2 分) 2分
A.
has used
B.
has been used
C.
was used
单选题 (2 分) 2分
A.
has used
B.
has been used
C.
was used
参考答案