人數限制 的英文怎麼說?

[1] a limit on the number of people[2] a limit to the number of people[3] a cap on the number of people[4] to cap the number of people

limit 跟 cap 都能指限制，作名詞用。

limit 跟 cap 也能作動詞用，例如:

We have to cap the number of applicants. = 我們必須對申請者設人數限制