SCHEMA:
CREATE TABLE table_name_76 (stage VARCHAR, young_rider_classification VARCHAR, intergiro_classification VARCHAR, points_classification VARCHAR)
USER:
During which stage was the Intergiro classification held by Miguel Indurain, the Points classification held by Mario Cipollini, and the Young rider classification held by Leonardo Sierra?

QUERY:
SELECT stage FROM table_name_76 WHERE intergiro_classification = "miguel indurain" AND points_classification = "mario cipollini" AND young_rider_classification = "leonardo sierra"