Select all the sources of the heat inside earth that are listed below.
a. mantle convection
b. earth's magnetic field
c. radioactive substances
d. lava on earth's surface
e. gravitational contraction
f. past bombardment by asteroids

Aremote community desperately needs more electrical energy. it is located in an area with the following characteristics: average wind speed of 15 – 20 km/hr some medium-sized rivers with slow-moving currents few coal deposits some oil exploration being conducted within 400 miles based on the above information, which energy source would be the most economical and safest for the community to pursue? a. fossil fuel b. hydroelectric c. nuclear d. wind