It’s a because b makes more since shown as the magnet
Density is mass over volume:

In your case, mass is 48 grams and volume is 12cm^3
If you put that into the equation, you will get your density:
Well the US doesn't naturally have a lot of fossil fuels so we rely on other countries who do have fossil fuels. So if we aren't that friendly with Saudia Arabia (they have a bunch of oil) then they can hike up the prices or cut us off from their oil supply completely which would cripple the US severly. So with that being said, we NEED other countries, and the big question is when will they not NEED us. At any point in which they feel that they don't need us they can just cut us off, which would be bad.
Hope that helps :)
Is this a book and most likely because the were cute