The base package including point class, line class, area class, volume class, complex object class and relation class, is the base of the application package and the combination package.

其中基础类包是应用类包和组合类包的基础，它用点、线、面、体、复杂对象和关系类等基本的要素表示三维空间。

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What might be less obvious is that it has been asking for permission to do that since 2009, during which time total mail volume has fallen more than 5% and First-Class volume has drop by more than 12%.

FORBES: First Class Mail is Doomed. Get Over it.

Charges taken in connection to a mandate to prefund retiree health care drove the loss in the latest quarter, but declining first-class and advertising mail volume were a drag on revenue.

WSJ: Postal Service Registers $5.2 Billion Loss

Interestingly, Class C properties are experiencing the largest increase in volume of applicants, as well as the largest effective rent growth.

FORBES: Property Managers Cut Renters Slack But At What Price?