题目

.  Nancy enjoyed herself so much ___ she visited her friends in Sydney last year. A. that                  B. since                 C. when                D. where 答案：C如图，PA、PB切⊙O于A、B两点，CD切⊙O于点E，交PA、PB于C、D，若⊙O的半径为r，△PCD的周长等于3r，则tan∠APB的值是__________．