human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Date/Location, Mens singles, Womens Singles, U21 Mens, U21 Womens, Mixed Restricted, Mixed Veteran
###Question: Who was the U21 Mens winner when Mike Marsden was the mixed restricted winner and Claire Nelson was the U21 Womens winner? 
gpt
SELECT U21 Mens FROM table WHERE Mixed Restricted = Mike Marsden AND U21 Womens = Claire Nelson