The phrase "He underlined that" is correct and usable in written English.
It can be used when emphasizing a point or statement made by someone.
Example: "In his speech, he underlined that the project deadline is non-negotiable."
Alternatives: "He emphasized that" or "He highlighted that."
He underlined that point by tweeting it at 11pm.
And he underlined that point in a later briefing.
He underlined that he feels "incredibly honoured by the Nobel prize," they added.
He underlined that the situations in Syria are stable in contrary to what is being broadcast by a number of western media, saying that the Syrian government has control on all aggravated regions like Aleppo.
He underlined that we thought the focus should be on the other shores of the Mediterranean and on breaking the link between getting in a boat and then getting settlement in Europe.
He underlined that South Africa further looked forward to working closely with the new Administration in the United States in promoting peace, security and prosperity around the world, especially on the African continent".
Sousa underlined that: he says his government was cautious not to turn Ontario in British Columbia or Alberta where private retailers mean Westerns can pick up liquor just about anywhere, and late at night and where "it costs almost six bucks more a two-four".
Adm Mullen says dumping DADT is "the right thing to do," although he underlines that he's speaking for himself and not the joint chiefs of staff as a whole.
He underlines that any solution agreed in negotiations must pass a Palestinian national referendum – though the documents reveal him admitting that it will not be possible to hold a vote outside the West Bank and Gaza, which would leave millions of refugees in Jordan and Lebanon unable to take part.
He supports making it more efficient to make the requests, which are often instrumental for child pornography investigations, but he underlines that there still needs to be some form of judicial authorization.
Anyway, he underlines that this technique is limited by the difficulty to study low-flow vessels and by the blooming artifact that tends to overestimate the smaller vessels.
