These are all words for sth that you say or write, especially sth that gives information or an opinion.以上各词均指口头或书面的说明、宣布。
statement something that you say or write that gives information or an opinion, often in a formal way通常指正式的说明、声明、陈述、报告：◆A government spokesperson made a statement to the press.政府发言人向新闻界发表了一份声明。
comment something that you say or write that gives an opinion on sth or is a response to a question about a particular situation指议论、评论、意见：◆She made helpful comments on my work.她对我的工作提出了有益的意见。
announcement a spoken or written statement that informs people about sth指公告、布告、通告：◆the announcement of a peace agreement和平协议公告
remark something that you say or write that gives an opinion or thought about sb/sth指谈论、言论、评述：◆He made a number of rude remarks about the food.他对这食物作了许多无礼的评论。
declaration(ratherformal) an official or formal statement, especially one that states an intention, a belief or a feeling, or that gives information指官方或正式的公告、宣告、宣言、声明：◆the declaration of war宣战
observation(ratherformal) a comment, especially one based on sth you have seen, heard or read尤指根据所见、所闻、所读而作的评论：◆He began by making a few general observations about the report.开头他先对这个报告作了几点概括性的评论。
comment, remark or observation?用 comment、remark 还是 observation？
A comment can be official or private. A remark can be made in public or private but is always unofficial and the speaker may not have considered it carefully. An observation is unofficial but is usually more considered than a remark. * comment 既可是官方的也可是私下的；remark 既可是公开的也可是私下的，但总是非官方的，说话者可能未经深思熟虑；observation 是非官方的，但通常较 remark 多几分考虑。
Patterns
a(n) statement/comment/announcement/remark/declaration/observation about sth