Read the given passage carefully and select the best answer to each question out of the five given alternatives.

Scientists have discovered massive mountains in the Earth’s mantle, an advance that may change our understanding of how the planet was formed. Most school children learn that the Earth has three layers: a crust, a mantle, and the core — subdivided into an inner and an outer core. While that is not wrong, it does leave out several other layers that scientists have identified within the Earth.

In a study published in the journal Science, scientists used data from an enormous earthquake in Bolivia to find mountains and other topography on a layer located 660 km straight down, which separates the upper and the lower mantle. Lacking a formal name for this layer, the researchers simply called it 'the 660-km boundary'. To peer deep into the Earth, scientists from the Princeton University in the U.S. and the Institute of Geodesy and Geophysics in China, used the most powerful waves on the planet, which are generated by massive earthquakes.

Data is collected from earthquakes that are magnitude 7.0 or higher which send out shockwaves in all directions that can travel through the core to the other side of the planet — and back again. For this study, the key data came from waves picked up after a magnitude 8.2 earthquake — the second-largest deep earthquake ever recorded — that shook Bolivia in 1994.