The Single Responsibility Principle (SRP)2 states that a class or module should have one, and only one, reason to change.

单一权责原则认为，类或模块应有且只有一条加以修改的理由。

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Customers who prefer not to purchase a recurring plan or sign a 2-year contract may instead purchase the device at full Suggested Retail Price (SRP) and utilize Sprint's pay-as-you-go services.

ENGADGET: Sprint offering free 3G / 4G Plug-in-connect, clears space for faster dongles