2.( 1) You can fill in (0,2,4,6,8).

(2) You can fill in (0,5).

(3) You can fill in (0)

3.( 1) Write three consecutive odd numbers (1, 3,5) and calculate their sum as (9). Is the total odd or even? (odd number)

(2) Write five consecutive odd numbers (1, 3, 5, 7, 9) and find their sum (25). Is the total odd or even? (odd number)

(3) Write seven consecutive odd numbers (1, 3, 5, 7, 9, 1 1, 13) and calculate their sum as (49). Is the total odd or even? (odd number)

Note: the answer to this question is not unique, but it is all odd.

4. It must be. For example:12345 =15,789101= 45.

The answer is guaranteed to be correct. I am a math teacher in the fourth grade of primary school.