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

### Instruction:
What is channel 33.7's official call sign?

### Inputs:
table_name: table, columns: ['Call sign', 'Analog channel', 'Digital channel', 'Virtual channel', 'Network', 'Station Ownership']

### Response:
SELECT Call sign FROM table WHERE Virtual channel = 33.7