Answer:
1, 2, 3, 4
or none
Explanation:
Mode is the value or values in the data set that occurs most frequently.
example:
For the data set 1, 1, 2, 5, 6, 6, 9 the mode is 1 and also 6.
in 1, 1, 2, 2, 3, 3, 4, 4 all numbers occur the same amount of times, therefore they all (or none) are the mode
hope this helps:)