question: Who was the U21 Mens winner when Mike Marsden was the mixed restricted winner and Claire Nelson was the U21 Womens winner? 
answer: SELECT u21_mens FROM table_28211674_3 WHERE mixed_restricted = "Mike Marsden" AND u21_womens = "Claire Nelson"
context: CREATE TABLE table_28211674_3 (u21_mens VARCHAR, mixed_restricted VARCHAR, u21_womens VARCHAR)