exist at the present time

However, it would take long time to realize this objective because at present the criterion of home intelligent network has not been unified and many technology problems still exist.

然而，目前家庭智能化网络的标准尚未统一，许多技术问题还有待于进一步解决，因此家庭网络化目标的实现仍然需要长期不断的努力。

Throughout most of Earth's history, glaciers did not exist, but at the present time about 10 percent of Earth's land surface is covered by glaciers.

在地球大部分的历史时期，冰川是不存在的，但是在现在，地球表面有大概10%的地方时被冰川覆盖的。

At the present time, there exist a lot of repetitive work in analysis of software reliability and safety which increase the software development cost.

目前，在软件可靠性与安全性的分析中产生很多重复性工作，增加了软件的开发成本。