Answer:
A. Elastic clause
Explanation:
The original draft of the constitution of United States only have four pages. It is impossible to write every single power that the government can have to run a country within those 4 pages. This is why an Elastic clause was created.
The elastic clause introduced the concept of "Necessary and proper"
Meaning that the constitution will laid out the main power and duty of the Congress. The Elastic clause granted the congress with the power to do additional actions that is deemed as "necessary" in order to fulfill its main duty. As long as those actions are "proper" , meaning not violating any other part of the constitution.