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    Some new oilfields since 1976. (A)were opened up (B)has opened up (C)have been opened up (D)had been opened up 【查看更多】

     

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    Some new oilfields ________ since 1976．

    [　　]
    A．

    were opened up

    B．

    has been opened up

    C．

    have been opened up

    D．

    had been opened up

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