I would go for the last one, as it is recommending Arnold Jones by giving two qualities or traits he possesses. Hope this helps, and let me know if you have any further questions.
Answer: I have known Arnold Jones for six years. He is smart and dependable.
A letter of recommendation is written by a previous employer, or a person close to the candidate (a teacher, supervisor, etc.) for the purpose of recommending them for an opportunity such as a job position, an internship, a scholarship or for college admission. The letter is meant to outline both the candidate's performance as well as his character and skills.
