Silicon in silca and many silcates has 4 oxygen near neighbours which are arranged in an approximately terahedral group around the central Si atom.
high porosity, low permeability
moderate porosity, low permeability
moderate porosity, low permeability.
Any form of water that falls to Earth's surface
The electron pairs in an ammonium ion are disposed along the four lines from the center of a tetrahedron to the four corners of the tetrahedron, with the nitrogen atom at the center of the tetrahedron.
Grassy plants cultivated for food is the most accurate description of grains.
Which description is not an accurate characterization of the Amazon River basin
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I am not a tetrahedron!
There is no more accurate descriptions of matter than measurements. To get the description right make your measurements precise.
Ruled by no one. (Mob)
Weak
a small group rulers
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changes in the reproductive system
Short and bloodless
manstor