Student drivers are required to keep a log of their supervised driving hours. However, not all students are diligent in their record-keeping. 
The transition that should be used to combine these sentences is the following one: however. This adverb is used to introduce a statement that contrasts with or appears to contradict something that has been previously said.  In this case, you are saying that student drivers should keep a written record of their supervised driving hours yet you are also stating that not all of them do it thoroughly and well.
 
        
                    
             
        
        
        
I should be D/the last one
        
             
        
        
        
Answer: A and B
Explanation: C is coming from your own ideas, and D is just not citing a source correctly. 
 
        
                    
             
        
        
        
Answer:
she supports her claim with reasons