Rare-earth metals are actually not as rare as once thought to be.
Answer the following statement true (T) or false (F)
True
Rare-earth elements are relatively plentiful in the Earth's crust, with one kind being as abundant as copper, but at low concentrations. Originally, rare earth minerals were mined in very few places, but in recent years new sources have been discovered and new mines are being developed to meet demand.
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Which of the following statements describes an important principle in the electrification of a cumulonimbus cloud?
A. Raindrops are always positively charged. B. Supercooled water is always negatively charged. C. Ice crystals are always negatively charged. D. Positive ions transfer from a warm object to a cold object.
Which of these is the greatest hazard?
A. The San Andreas Fault B. global warming C. Mauna Loa D. Mt. St. Helens
Earth emits radiation with greatest intensity at ____ wavelengths
A) infrared B) radio C) visible D) ultraviolet
The structure of epidermal growth factor includes which of the following?
A) four helical segments B) only b-pleated sheet C) both a-helix and b-pleated sheet D) four cysteine residues which form two disulfide bridges