Technology is developing so rapidly that ________ for only a year, my cell phone is out of date．

1. A.
   using
2. B.
   having been used
3. C.
   having used
4. D.
   is using

Technology is developing so rapidly that _____ for only a year, my cell phone is out of date.   

  A. using          B. having been used    C. having used     D. is using