CREATE TABLE table_name_15 (mountains_classification VARCHAR, general_classification VARCHAR, winner VARCHAR)

What's the mountains classification of winner Carlos Sastre when the general classification is Denis Menchov?
SELECT mountains_classification FROM table_name_15 WHERE general_classification = "denis menchov" AND winner = "carlos sastre"
SELECT "mountains_classification" FROM "table_name_15" WHERE "carlos sastre" = "winner" AND "denis menchov" = "general_classification"