CREATE TABLE table_73699 ("Outcome" TEXT, "Year" FLOAT, "Championship" TEXT, "Surface" TEXT, "Partner" TEXT, "Opponents" TEXT, "Score" TEXT)

When us open (2) is the championship what is the surface?
SELECT "Surface" FROM table_73699 WHERE "Championship" = 'US Open (2)'
SELECT "Surface" FROM "table_73699" WHERE "Championship" = 'US Open (2)'