How much of the world's diversity is threatened as tropical forests are converted to agricultural use?
20 percent
30 percent
40 percent
50 percent

for example, no new evidence will demonstrate that the earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the earth is not divided into solid plates that have moved over geological timescales .