题目

On “Super Bowl Sunday”, millions of Americans are glued to their TVs. They are eating pizza, chicken wings and chips and cheering every move. They’re watching the Super Bowl. Why are Americans so crazy about American football? Well, it is more exciting than other sports. One team can lose possession of the ball in a minute, which may allow their opponents to make a touchdown(触地得分). Then that team may win the game unexpectedly. The Super Bowl also entertains its audience with a great halftime show. The football field is turned into a stage. Then an impressive performance of7．如图，四边形ABCD内接于⊙O，若∠A：∠C=5：7，则∠A=75度．