Which Opponent has a Game site of heinz field, and a Record of 3 1?
CREATE TABLE table_74818 (
    "Week" real,
    "Date" text,
    "Kickoff (ET)" text,
    "Opponent" text,
    "Result" text,
    "Record" text,
    "Game site" text,
    "NFL Recap" text
)
SELECT "Opponent" FROM table_74818 WHERE "Game site" = 'heinz field' AND "Record" = '3–1'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: Which Opponent has a Game site of heinz field, and a Record of 3 1? ### Input: CREATE TABLE table_74818 (
    "Week" real,
    "Date" text,
    "Kickoff (ET)" text,
    "Opponent" text,
    "Result" text,
    "Record" text,
    "Game site" text,
    "NFL Recap" text
) ### Response: SELECT "Opponent" FROM table_74818 WHERE "Game site" = 'heinz field' AND "Record" = '3–1'