The newly learnt words will soon be forgotten ________ frequently used in everyday communication．

1. A.
   if they are
2. B.
   unless they are
3. C.
   when they are
4. D.
   till they are

-- I can’t remember the English words I learnt yesterday.

--You know, the newly learnt words will soon be forgotten ______ frequently used in everyday communication.

A. if                     B. unless                 C. when                 D. till