Very helpful thread. Always handy to have a reminder about how to phrase a letter.
I would just like to point out though that in “Civil Engineering” cover letter, it starts with “I write” – to me that is wrong, as it is obvious you are writing, as it is a letter. I was told this a long time back that job application letters should never start with “I am writing to apply” as obviously you are writing. It is possible it has changed now, but I still feel it is incorrect.