The answer is D. Gravity.
Gravity attracts objects to the surface of the Earth. Take a falling brick, for example, the brick has more mass, therefore, there is more attraction between the brick and Gravity. The brick is a solid object and is heavier as well.
Hope this helps! :)
To figure out just where that earthquake happened, you need to look at
your seismogram and you need to know what at least two other
seismographs recorded for the same earthquake. You will also need a map
of the world, a ruler, a pencil, and a compass for drawing circles on
the map.
