Which sentence is the correctly written simple sentence? 
 A. Gettysburg is a Civil War battlefield and so is Antietam. 
 B. Gettysburg is one Civil War battlefield Antietam is another. 
 C. Gettysburg and Antietam are both Civil War battlefields, and I have toured them both. 
 D. Gettysburg and Antietam are Civil War battlefields.