The collection of vowels in English alphabets. This set contains five elements. Namely, `a ,\ e ,\ i ,\ o,\ u.`

Explanation

As set is a well defined collection of objects. Therefore collection of vowels in English alphabets can contains five elements `a ,\ e ,\ i ,\ o,\ u.`.which can be written as

C={a,e,i,o,u.}

which is well defined.
Hence the collection of vowels in English alphabets which contains five elements, `a ,\ e ,\ i ,\ o,\ u.` is set.