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______ we are doing has never been done before.

    A. That               B. What

C. Which              D. Whether

_______ we are doing has never been done before.

    A. That               B. What

    C. Which              D. Whether

_______ we are doing has never been done before.

A. That　　　　　　　　　　 B. What

C. Which　　　　　　　　　　 D. Whether

____we are doing has never been done before.
A. That  　　 B. Which　　　  C. whether　　　　　  D. What

_______ we are doing now has never been done before.?

A. That B. What?

C. Which D. Whether?