The correct option is C Diary entry
The correct format is Option D. The challenges faced by an individual are personal. It may also include some personal emotions which made the day challenging for that individual. So, 'a very challenging day at work' should be written as a diary entry. Options B and C are incorrect as journals and articles are used to express news for public interest. Option A is incorrect as a report is a systematic and well organized presentation of facts and findings of an event that has already taken place somewhere.