It is unlikely that Gertrude is a wolf. It is highly unlikely that Bernhard is a frog. It is likely that John went to the garden. It is unlikely that if John went to the garden, and Bernhard is a frog, then Greg is a swan. Chances are about even that if Bernhard is a frog, and John went to the garden, then Brian is gray. It is impossible that if either John went to the garden, or Gertrude is a wolf, then Bill dropped the milk.
There is almost no chance that either Brian is gray, or Bill dropped the milk.
There is almost no chance that either Brian is gray, or Bill dropped the milk.
It is almost certain that either Brian is gray, or Bill dropped the milk.
Either Brian is gray, or Bill dropped the milk.