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题目内容
（江苏开放大学大学英语（B）作业1）
A-13. Sales of CDs have greatly increased since the early 1990s, when people _____ to enjoy the advantages of this new technology.
A
begin
B
began
C
have begun
D
had begun
A
begin
B
began
C
have begun
D
had begun
参考答案
