Unless they are programmed by humans, computers are nothing more than big pieces of metal. But once____ what to do , they show extraordinary power in carrying it out.

　　A. taught B. teaches C. teaching D. to teach

Unless they are programmed by humans, computers are nothing more than big pieces of metal. But once _____ what to do, they show extraordinary power in carrying it out.

1. A.
   taught
2. B.
   teaches
3. C.
   teaching
4. D.
   to teach

Unless they are programmed by humans, computers are nothing more than big pieces of metal. But once _____ what to do, they show extraordinary power in carrying it out.

  A. taught   B. teaches    C. teaching      D. to teach