There are two basic systems for issuing certificates: a closed (private hierarchy) system and an open (public hierarchy) system.
发布证书有两种基本的系统：封闭式(私有层次)系统与公开式(公共层次)系统。
The glacial system is governed by two basic climatic variables: precipitation and temperature.
冰川系统由两个基本的气候变量控制：降水和温度。
This is a trivial example and focuses on two simple bottlenecks, but it highlights the basic advantages of having access to system performance information.
虽然这是一个很小的示例，侧重的也只是两个简单的瓶颈，但是它突出了访问系统性能信息的基本优势。
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