________ is known to all, good friends ________ happiness and value to life.

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________ is known to all, good friends ________ happiness and value to life.

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________ is known to all that good friends ________ happiness and value to one's life．

1. A.
   It; add
2. B.
   As; add
3. C.
   It; add up to
4. D.
   As; add to

______ is known to all is that good friends ______ happiness and value to life．

   A.What；add to             B. It；add                    C. What；add             D. It；add to

        is known to all is that good friends        happiness and value to life．

A．What；add to         B．It；add                   C．What；add             D．It；add to