Answer with explanation:
When you talk about numbers, and the people who are aware of numbers , after knowing natural numbers and whole numbers , decimals came into existence because fractional value were being used that's why rational number was a set of numbers which came into existence.
So, why after natural number, whole number , was formed, because 0 which means nothing, was extremely useful number and added to set of natural numbers.
Then People started using Decimals, that is fractional number,
⇒Apart from, application of symmetry, as all the options are true regarding number sense,
So, Decimals was used or invented , after knowing about whole numbers and natural numbers
So, Key area of Number Sense is,
Option D: Use of Decimals