Задание 7. Выберите верный ответ

The inscribed angle subtended by the arc AC is ∠ABC. The central angle subtended by the same arc is ∠AOC. From the diagram, ∠ADC = 120°. Since ABCD is a cyclic quadrilateral, opposite angles sum to 180°. Therefore, ∠ABC + ∠ADC = 180°. So, ∠ABC = 180° - 120° = 60°.