Visibility is quite poor when car windows keep ____ up.

verb

1. To cover, envelop, or suffuse with or as if with fog

   "fog the barns with pesticide"

2. To make obscure or confusing

   "accusations which fogged the real issues"

3. To make confused
4. To produce fog on (something, such as a photographic film) during development
5. To become covered or thick with fog
6. To become blurred by a covering of fog or mist
7. To become indistinct through exposure to light or radiation