Where did Dickens get the idea to write A Tale of Two Cities?

How to Cite the "Where did Dickens get the idea to write A Tale of Two Cities?" from CliffsNotes.com:

CliffsNotes.com. Where did Dickens get the idea to write A Tale of Two Cities? 23 Nov 2009
<http://www.cliffsnotes.com/WileyCDA/Section/id-305403,articleId-27102.html>.

Back to Where did Dickens get the idea to write A Tale of Two Cities?