C. a basic index, while the other resources are full databases allowing access to actual articles.
The Readers' Guide to Periodical Literature is just that - a guide. This means that it works as an index that a person would use for finding resources. It is not an actual database with full articles. EBSCOhost and Expanded Academic ASAP are online databases that allow the researcher access to full articles. Option B is wrong because it just is wrong as a statement an older index is not more comprehensive since it's missing the newer resources. Option A is also an incorrect statement.