Using Prolog, I first created two facts called grade and food: The first fact is grade(X,Y) where X is the student (rob or matt) and Y is the grade level (freshman or sophomore). The second fact is food(X,Y) where X is the student (rob or matt) and Y is the food (pizza, burger, pasta, wrap).

I created a rule called preference(X,Y), where X is the student (rob or matt) and Y is the students' preference.

I want to enter `preference(rob,X).` in the GNU Prolog and have it return:

sophomore, pizza, burger.

However, it keeps returning: sophomore, pizza, pizza.

How do I fix this problem? I've spent hours looking into this. Thanks

This is the code I have:

```
grade(rob, sophomore).
grade(matt, freshman).
food(rob, pizza).
food(rob, burger).
food(matt, pasta).
food(matt, wrap).

preference(X,Y):-
   grade(X,A),
   food(X,B),
   food(X,C),
   Y = (A, B, C).

```