What is the IcAO of Frankfurt?
CREATE TABLE table_name_91 (
    icao VARCHAR,
    city VARCHAR
)
SELECT icao FROM table_name_91 WHERE city = "frankfurt"
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: What is the IcAO of Frankfurt? ### Input: CREATE TABLE table_name_91 (
    icao VARCHAR,
    city VARCHAR
) ### Response: SELECT icao FROM table_name_91 WHERE city = "frankfurt"