— I wonder how much you charge for your services．
— The first two are free _______the third costs $30．

— I wonder how much you charge for your services．

— The first two are free _______the third costs $30．

A．while             B．until　　          C．when             D．before

— I wonder how much you charge for your services．

— The first two are free _______the third costs $30

A. while                   B. until　　           C. when            D. before

— I wonder how much you charge for your services．
— The first two are free _______the third costs $30．

1. A.
   while
2. B.
   until　　
3. C.
   when
4. D.
   before