单语范例（未经PONS编辑处理）
Occurrence is rare in children and people under 40 but peaks between 40 and 70 years of age.
en.wikipedia.org So listed because its extent of occurrence is, in fact, not much greater than 100 km -- it is known from only four small islands.
en.wikipedia.org Most of the tungsten mineralization is wolframite with a number of small scheelite occurrences known.
en.wikipedia.org It has an occurrence range of 31700000km2 sqmi and a breeding range of 13km2 sqmi.
en.wikipedia.org However, these two incidents are probably not as much of a freak occurrence as they appear to be.
en.wikipedia.org