At a gathering of 30 people, there are 20 people who all know each other and 10 people who know no one. People who know each other hug, and people who do not know each other shake hands. How many handshakes occur?<spanclass=′latex−bold′>(A)</span>240<spanclass=′latex−bold′>(B)</span>245<spanclass=′latex−bold′>(C)</span>290<spanclass=′latex−bold′>(D)</span>480<spanclass=′latex−bold′>(E)</span>490