Sentence 1: Dan's guitar distorted when he plugged it in. 
 Sentence 3: Dan found the grounding in the plug was bad 
 Sentence 4:  He called an electrician to fix it 
 Sentence 5:  Now Dan's guitar isn't distorted 
 Option 1: He checked the grounding but it was fine. 
 Option 2: He looked for the source of the problem.