i though that is <del> not <s> so i choosed underline

Answer 1

Visually, both <del> and <s> strike the text in between, but <s> has been deprecated in HTML5, and <del> adds some semantic information. I encourage to use <del>. Underline is for other purposes, though.
https://www.w3schools.com/tags/tag_del.asp
https://www.w3schools.com/tags/tag_s.asp