Read the following context and choose the best option to answer the question.
Context: It 's keeping opponents from light up the scoreboard that 's been the problem in Cincinnati . The Bengals have made a collective effort to improve their defense in the past three drafts , using their last three first round picks on that side of the ball . In 2006 , Cincy selected South Carolina corner Jonathan Joseph with their first round pick and in 2007 the Bengals took another defensive back with their first pick in Michigan 's Leon Hall . This past draft , the team tabbed USC outside linebacker Keith Rivers in the first round .
Question: What is the reason the Bengals keep losing ?
Options: 
A. Jonathan Joseph stayed with South Carolina .
B. Keith Rivers remained at USC
C. Leon Hall stayed at Michigan .
D. Their defense needs improving .


D