CREATE TABLE table_name_8 (surface VARCHAR2, opponent_s_ VARCHAR2)

Which Surface has an Opponent(s) of anna-lena gr nefeld tatjana malek?
SELECT surface FROM table_name_8 WHERE opponent_s_ = "anna-lena grönefeld tatjana malek"
SELECT "surface" FROM "table_name_8" WHERE "anna-lena grönefeld tatjana malek" = "opponent_s_"