Explanation:
1. The universe consisted of hydrogen and helium initially. This statement is true.
2. It is important to understand radioactive decay in order to understand this question, here's a good analogy:
A snake will shed it's skin, just as an atom will shoot off different parts of itself. It would be very difficult to force that snake to reenter it's skin once it sheds, just as it takes a lot of energy to force <em>fusion</em><em> </em>of atoms and the parts mentioned. In normal circumstances, nuclear decay is one-way.
3. The earth is a giant floating rock in space. It took many many years to gather a bunch of asteroids and dust to make this planet.
4. I shouldn't have to explain this one, it doesn't make much sense.
Answer: D
Explanation: Gaseous composition, larger size and many moons
If an object is at equilibrium, the net force acting upon the object is 0 Newton.
