There _______ a lot of changes in Beijing since the 2008 Olympic.横线上填have been 还是are请说明原因,谢谢

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There _______ a lot of changes in Beijing since the 2008 Olympic.横线上填have been 还是are请说明原因,谢谢
There _______ a lot of changes in Beijing since the 2008 Olympic.横线上填have been 还是are
请说明原因,谢谢

There _______ a lot of changes in Beijing since the 2008 Olympic.横线上填have been 还是are请说明原因,谢谢
have been
since(自从)用于完成时态中,主句好为完成时态.

have been,since后的从句前一句是完成式

are
there be 句型

have been

have been 因为since the 2008 引导的时间状语额!