Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Who is the call sign that has a commenced operation before 1976?

### Inputs:
table_name: table, columns: ['AIRLINES', 'IATA', 'ICAO', 'CALLSIGN', 'COMMENCED OPERATIONS']

### Response:
SELECT CALLSIGN FROM table WHERE COMMENCED OPERATIONS < 1976