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

### Instruction:
What class has less than 12 numbers built operated by southern?

### Inputs:
table_name: table, columns: ['Class', 'Operator', 'No. Built', 'Year Built', 'Cars per Set', 'Unit nos.']

### Response:
SELECT Class FROM table WHERE No. Built < 12 AND Operator = southern