Sentence 1: Derek was only six when he began to get sick. 
 Sentence 3: The operation was a success but left a huge scar on his head 
 Sentence 4:  Derek worried his classmate would make fun of him 
 Sentence 5:  So he dad went and got a tattoo on his head matching the scar 
 Given Sentence 2: It turns out he had a brain tumor and had to get an operation.