Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
```
you may use the attached model cancellation form , but it is not obligatory . 

```
. OPTIONS: ['Jurisdiction' 'Arbitration' 'None' 'Contract by using'
 'Unilateral termination' 'Unilateral change' 'Content removal'
 'Choice of law' 'Limitation of liability'].