There reach into everyday Americans.
A primary example of a primary source, ironic wording there.
Would be first hand accounts, documents, journals, text, anything from the era or timeframe where the subject is from.
Ex: Revolutionary War
Primary Source: George Washington's speeches
Answer:
Compass: Allowed sailors and navigators to find direction.
Gunpowder: Allowed us to make modern day weapons, such as guns.
Paper: Allowed us to write on a thing that can be mass produced and is efficient to use.
Explanation:
The answer is A, C & D make no sense. B is not wrong, but A is the better answer.
I have to say B. The rest were concepts made in Greece, by Greek philosophers, politicians, or mathematicians. An example for an advancement in math is the Pythagorean Theorem. I hope this helps!