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题库 / OG2017Q-PS-173
If x, y, and z are positive integers such that x is a factor of y, and x is a multiple of z, which of the following is NOT necessarily an integer?
~$x+z \over z$~
~$y+z \over x$~
~$x+y \over z$~
~$xy \over z$~
~$yz \over x$~
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