Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
```
any promotion code or offer provided by us may not be used in conjunction with any other promotion code or offer , past or present . 

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