The correct option is
A Sunday, 10th January, 20XX
Diary entry is a personal and informal document. It records an individual's account of a day of his/ her life. On the top left corner of the diary entry, the day and date have to be written. Hence, blank no. 26, has to be filled with the day and date.
The format of the date is:Date (Eg: 24th) month (name of the month), and year (in four digits). Hence, the correct format for recording the day and the date is: Sunday, 10th January, 20XX and option A is correct. Option D is incorrect as the word, 'Today' is not written in the beginning of the diary entry. However, the word, 'today' can be used to begin the sentence which describes the events of the day or the writer's feelings.
The words, 'To diary' and 'To me' are not written in separate lines in a diary entry. Hence, options B and C are correct.