CREATE TABLE table_4233 ("Pick #" FLOAT, "MLS team" TEXT, "Player" TEXT, "Position" TEXT, "Affiliation" TEXT)

what is the position for the united states u-20 affiliation
SELECT "Position" FROM table_4233 WHERE "Affiliation" = 'United States U-20'
SELECT "Position" FROM "table_4233" WHERE "Affiliation" = 'United States U-20'