time is useful

First of all, many pupils suggest that history is one of the less interesting school subjects and that governments should spend the time and money on subjects that are more useful.

首先，许多学生认为历史是一门不那么有趣的学校科目，政府应该把时间和金钱花在更有用的科目上。

A credible inflation target of 2 or 3 per cent, maintained over a credibly long period of time, is useful.

在相当长的一段时期内，维持2%或3%这种可靠的通胀率目标，是有用的。

But taking even short periods of time off is useful. Here's what I suggest you to do.

但是，一小段时间的休假也是有效的。