In default logic, which of the following inference rules of the form is allowed? A. (A : B) / C B. A / (B : C) C. A / B D. A / B : C

The correct answer is: A. (A :

In default logic, a default rule is a rule of the form (A : B) / C, which means that if we know that A is true, then we can conclude that B is true, unless we know that C is true.

For example, the default rule (Bird : Fly) / (Not-In-A-Cage) means that if we know that something is a bird, then we can conclude that it flies, unless we know that it is in a cage.

The other options are not allowed in default logic. Option B, A / (B : C), is not allowed because it does not allow for the possibility that C is true. Option C, A / B, is not allowed because it does not allow for the possibility that B is false. Option D, A / B : C, is not allowed because it does not allow for the possibility that C is true.