"underline them" is a correct and usable part of a sentence in written English.
You can use it to refer to the act of underlining words or phrases on a page. For example: "Please read these instructions closely and underline them if you need to refer back to them later."
"I read things and underline them.
"If you want to bless someone, you chew on this hot pepper, and it is believed that the heat of the pepper on the tongue will go into your words and spiritually underline them," he said.
In Skype, the company showed off rich Cortana integration which put the assistant directly into the app where she could help users do things like identify the persons, places and things in your messages, underline them, and then display more info in a card-like interface when clicked.
I would literally cut out his columns, underline them, and learn them by heart.
In the books that simply take place in the past, King can give us a plethora of details: the duck's-ass haircuts, the slang, the old cars like Sunbeams and Chryslers, the dated racism but he can't underline them with the characters' reactions as he does with his time traveler in 11/22/63.
Adding underscores around word(s) will automatically underline them.
(She clipped his columns from the paper, underlined them, and saved them in a special file).
The abject poverty of Thursday night's Europa League defeat in Denmark merely underlined them.
LeCompte doesn't comment on the racism of O'Neill's language or ideas by underlining them with a strident moral stance.
(When he did, he coded the passages divided by parentheses by underlining them with colored pencils so that he could follow the thread).
The New York Philharmonic's Ives festival is an odd, not unpleasant collage, juxtaposing snippets of Ives and other composers to postulate connections rather than underlining them.
