human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Name or route, type, elevation groundstation, elevation mountainstation, slope length, capacity in persons/hour, construction year(s)
###Question: Which slope length has a type of surface lift, and an elevation groundstation smaller than 1974, and a construction year(s) of 1971, and a Name or route of alpmatten 1?
gpt
SELECT slope length FROM table WHERE type = surface lift AND elevation groundstation < 1974 AND construction year(s) = 1971 AND Name or route = alpmatten 1