支持某人做某事可以用以下几种英语表达方式：

1. Support sb. in doing sth. 例如：I support him in his decision to study abroad.

   

2. Support sb."s decision/choice to do sth. 例如：I fully support her choice to pursue a career in music.

3. Be in favor of sb. doing sth. 例如：I am in favor of them starting their own business.

4. Back sb. up in doing sth. 例如：I’ll back you up in your efforts to improve the community.

5. Encourage sb. to do sth. 例如：We should encourage more young people to engage in volunteer work.

6. Stand by sb. as they do sth. 例如：I will stand by you as you take on this new challenge.

每种表达方式都有微妙的差别，但都传达了支持某人做某事的意思。