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

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)'