名詞性從句主語從句：主語從句，表語從句，賓語從句。
    1. we will do next is still under discussion.
    A. That
    B. When
    C. Where
    D. What
    2. was once regarded as impossible has now become a reality.
    A. That
    B. Which
    C. Who
    D. What
    3. _______ books you borrow from the library should be returned in two weeks’ time.
    A. Whatever
    B. Which
    C. No matter what
    D. What
    4. she will be given this job is still under discussion.
    A. Although
    B. Whether
    C. If
    D. What
    5. He found at last ______ he had been looking for.
    A. that
    B. what
    C. where
    D. which