Final answer:
The word group that should end with a hyphen is 'post WWII'.
Step-by-step explanation:
The word group that should end with a hyphen is post WWII. When we combine the words 'post' and 'WWII' to describe books on life after World War II, we use a hyphen to show that they are functioning together as a compound adjective.
Learn more about Using hyphens in compound adjectives