Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
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for the purposes of our monthly and yearly subscriptions , a month constitutes 30 calendar days , a year constitutes 365 calendar days and two years constitutes 730 calendar days . 

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