I would go with Readers' Guide, because it lists hundreds of magazines. Usually, there is a reference list for all the available magazine articles that is arranged alphabetically by subject. This is called a reader's guide. A newspaper index is a reference for newspapers base on the issue date while a card catalog is a reference in finding authors of books. So the correct answer is C. I hope this answer helped you <3
Well if you want to self check you have to know what are the keys to answer
Answer:
Seven hours after a nuclear explosion, residual radioactivity will have decreased to about 10 percent of its amount at 1 hour, and after another 48 hours it will have decreased to 1 percent.