A ‘Source’ refers to the actual source from where the visitor was referred to your site. Among the options, ‘Email’ is not a source, it is a Medium. ‘googlemerchandisestore.com’ is a source, ‘Google’ is a source and ‘(direct)’ is also a Source.
This question is a part of the Google Analytics Individual Qualification. You can get all the answers with detailed explanation for this exam in our Google Analytics Individual Qualification Exam Answers page.