CREATE TABLE table_46943 ("Year" FLOAT, "Men's Open" TEXT, "Women's Open" TEXT, "Mixed Open" TEXT, "Men's u20" TEXT, "Women's u20" TEXT, "Senior Mixed" TEXT, "Men's 30" TEXT, "Women's 30" TEXT, "Men's 35" TEXT, "Women's 35" TEXT, "Men's 40" TEXT, "Women's 40" TEXT, "Men's 45" TEXT, "Men's 50" TEXT)

Which Men's u20 has a Men's 45 of n/A?
SELECT "Men's u20" FROM table_46943 WHERE "Men's 45" = 'n/a'
SELECT "Men's u20" FROM "table_46943" WHERE "Men's 45" = 'n/a'