题目

 如图，已知⊙O中∠AOB度数为100°，C是圆周上的一点，O    则∠ACB的度数为(     )B      A.130°      B.100°     C. 80°       D. 50°          A   答案：AThe U.S. President Barack Obama arrived in China's economic center Shanghai on Sunday nightof November 15th 2009, ______a state visit to China. [     ]A. starting B. started C. to start D. having started