A: 69 ÷ 3 = 23, and the adjacent three numbers are 22, 23 and 24.
Since 1 is Monday, 22, 23 and 24 are Monday, Tuesday and Wednesday.
B:54÷3= 18, and the three adjacent numbers are 17, 18 and 19.
Since 1 is Monday, 17, 18 and 19 are Wednesday, Thursday and Friday.
C:27÷3=9, and the adjacent three numbers are 8, 9 and 10.
Since 1 is a Monday, 17, 18 and 19 are Mondays, Tuesdays and Wednesdays.
In short:
The sum of three adjacent numbers or a multiple of three.
And d is obviously not a multiple of 3.