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

### Instruction:
What's the period of a rock album released in 1973?

### Inputs:
table_name: table, columns: ['Artist', 'Country of origin', 'Period active', 'Release-year of first charted record', 'Genre', 'Claimed sales']

### Response:
SELECT Period active FROM table WHERE Release-year of first charted record = 1973 AND Genre = rock