Measures have been taken to solve the problem, but it may be some time ____ the situation improves.

A. since　　 B. when　　 　 C. unless 　 D. before

Measures have been taken to solve the problem, but it may be some time ________ the situation improves．

1. A.
   since
2. B.
   when
3. C.
   before
4. D.
   unless

Measures have been taken to solve the problem, but it may be some time ____ the situation improves．

       A．since           B．when           C．unless     D．before