Describe an easy technique to judge whether the correct pronoun is being used as a compound subject in the example sentence below. Example sentence: Me and Frank thought it would be a good idea to review before the test.

If either part of the compound subject can be used (correctly) as a subject by itself, then it will work in a compound subject as well.

Explanation:

Me and Frank thought it would be a good idea to review before the test.

Frank works, but does Me?

Me thought it would be a good idea to review before the test.  

No, it should be

I thought it would be a good idea to review before the test.

And then we never put ourselves first in a compound subject, so the correct compound subject would be

Frank and I thought it would be a good idea to review before the test.

answer: the prince warns the 2 families that if they get into another fight they will be put to death