Answer:
A: Helium or Hydrogen
Explanation:
Terrestrial planets are the 4 inner most planets of the solar system which are mercury, venus, earth, Mars, while the giant planets are the 4 outer most which are Jupiter, Saturn, Uranus and Neptune.
Now, these outer most ones are the surface ones and are surrounded primarily by layers of hydrogen and helium gases.
I think it’s A because each unit is worth 3
Answer:J.J. Thomson, he was using a high-vacuum cathode-ray tube
Explanation:(I Googled it)
That would be correct as stated.