I usually sleep with the window open _____ it’s very cold.

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

I usually sleep with the window open _____ it’s very cold.

1. A.
   until
2. B.
   unless
3. C.
   when
4. D.
   if

I usually sleep with the window open ________ it's very cold.

1. A.
   until
2. B.
   unless
3. C.
   as
4. D.
   if