科研之友
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<正>Friday the 13th is considered a day in which bad things oc-cur. It is a superstition. A superstition is a belief of somethingominous(不祥的)without actual reason.The origin of this superstition is unclear. Both Friday and thenumber 13 have been considered unlucky for hundreds of years.Bad luck associated with the number 13 may have something to do
