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