The answer would be small nonmetal atoms
Answer: A Ruler
Explanation:A Ruler is a common instrument used for measuring the length of small objects. It usually has four units of measurement to choose from: millimeter, centimeter, inch, and foot.
Answer:
I would say discovering who invented the radio.
Explanation:
The other ones can be solved by experiments and the "discovering who invented the radio" cannot be solved by an experiment.
hope this helps.