CREATE TABLE table_50811 ("Edition" CLOB, "Round" CLOB, "Date" CLOB, "Against" CLOB, "Surface" CLOB, "Opponent" CLOB, "Result" CLOB)

what is the surface when the opponent is selma babic?
SELECT "Surface" FROM table_50811 WHERE "Opponent" = 'selma babic'
SELECT "Surface" FROM "table_50811" WHERE "Opponent" = 'selma babic'