设S、R、T三点为一等边三角形的三个顶点,X、Y、Z为ASRT三边的中点。若用此六个点中的任意三个点作顶点,可有多少种面积不等的三角形?( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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