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

### Instruction:
What is the average year to begin making autos for a brand that joined GM in 1917?

### Inputs:
table_name: table, columns: ['Brand', 'Year founded', 'Year began making autos', 'Year joined GM', 'Markets served today']

### Response:
SELECT AVG Year began making autos FROM table WHERE Year joined GM = 1917