Who was Mountains Classification in the race with Nick Frey as Youth Classification and Tom Zirbel as Points Classification?
CREATE TABLE "classification_leadership_progress_table" (
  "stage" real,
  "winner" text,
  "general_classification" text,
  "mountains_classification" text,
  "points_classification" text,
  "youth_classification" text,
  "team_classification" text
);
SELECT "mountains_classification" FROM "classification_leadership_progress_table" WHERE "youth_classification"='Nick Frey' AND "points_classification"='Tom Zirbel';