他解释了拥有无线网络连接的有用性。

He explained the ___usefulness of having a wi-fi connection.

他们昨天回来了，我采访了他们，以了解他们对这个项目有用性的看法。

They came back yesterday and I have interviewed them to find out what they think about the ___usefulness of the programme.

这个工具在日常任务中的有用性怎么强调都不为过。

The ___usefulness of this tool in daily tasks cannot be overstated.