Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_23157997_13 (mountains_classification VARCHAR, youth_classification VARCHAR, points_classification VARCHAR)
### Question:
Who was Mountains Classification in the race with Nick Frey as Youth Classification and Tom Zirbel as Points Classification?
### Answer:
SELECT mountains_classification FROM table_23157997_13 WHERE youth_classification = "Nick Frey" AND points_classification = "Tom Zirbel"