有必要的英文是:oblige;be necessary。
1、也许有必要对这个设计稍作几处修改。
It might be necessary to make a few slight modifications to the design.
2、可能有必要将酱汁稍稍稀释一下。
It may be necessary to thin the sauce slightly.
3、有必要对儿童进行吸毒危害的教育。
Children need to be educated on the dangers of drug-taking.
4、有必要彻底改革税制。
A radical overhaul of the tax system is necessary.
5、有必要使讨论的焦点更加集中。
There is a need to sharpen the focus of the discussion.
6、如果有必要,我们会再次和你联系。
We will contact you again if the need arises.