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

### Instruction:
Which class has a year prior to 2011 and audi r15 tdi as the chassis?

### Inputs:
table_name: table, columns: ['Year', 'Entrant', 'Class', 'Chassis', 'Engine', 'Rank', 'Points']

### Response:
SELECT Class FROM table WHERE Year < 2011 AND Chassis = audi r15 tdi