题目

—Her concert was ________ big success last night. —I think it surely makes ________ difference for a new talent. A . /; / B . a; a C . a; the D . a; / 答案：B（1999•海淀区）已知：如图，在⊙O中，CD过圆心O，且CD⊥AB，垂足为D，过点C任作一弦CF交⊙O于F，交AB于E．求证：CB2=CF•CE．