The phrase "they commented" is grammatically correct and can be used in written English.
Example: After reading the article, they commented on how informative and well-written it was.
Sometimes they commented on my weight.
They commented on the youth of India, Indonesia & Japan.
They commented on the health care, wages, and solid training provided through the apprenticeship system.
When they shared their impressions with colleagues, they commented on how unconcerned the president seemed.
Yet the choreographers also provided program notes in which they commented on their sources of inspiration.
It is unclear whether they commented later in the game on Mr. Rector's lengthy nap.
Disappointingly, although they commented favourably on some aspects, their general view was that the situation had not improved.
On Sunday, opposition leaders denounced the mass trial as illegitimate, though they commented before Mr. Mortazavi warned about possible prosecutions.
They commented to him, "Wow!
They commented that postsurgical distraction of the condyle was consistently associated with relapse.
On their Facebook page, they commented: "It is being dealt with.
