The are all the counting numbers.
select one:
a. integers
b. real numbers
c. absolute values
d. natural numbers

It cannot be be Integers because Integers include negative numbers (which are not counting numbers)

It cannot be real numbers because like integers, it includes negative numbers but also includes decimals which are not counting numbers

It cannot be absolute values because absolute values is the range of how far away a number is from 0 which obviously isn't counting

That leaves natural numbers which are counted in sequence which fits the definition needed

D. Natural Numbers