The government, when necessary, has recourse to the armed forces.

政府在必要时可以动用军队。

They are not afraid to tackle the issues or let the sparks fly when necessary.

他们不怕应付这些问题, 必要时也不惜进行唇枪舌剑的激烈争论。

With any container that you choose, you need to ensure that it allows the water in it to drain when necessary.

对于您选择的任何容器，您需要确保在需要的时候它能够排除里面的水。

When necessary, instinct is the most reliable resource you can fall back on.

必要时，本能是你可使用的最可靠的资源。

Only flush the toilet when necessary: this means to not use the toilet as a garbage to avoid wasting water.

只在必要时冲厕所：这意味着不要把厕所当作垃圾桶使用以避免浪费水。