The program has a Tier system that is based on the length of continuous subscription. This means that the longer you stay subscribed, the higher your Tier. You will not be able to buy the Tiers directly and will only have to stay subscribed to meet each criterion to be upgraded.
Please see the table below for the months of continuous subscription needed to reach each Tier:
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FarmVille 2: Country Escape Game GUIDE
哈利波特：巫師聯盟