Which of the following sets contains an element that cannot be classified as rational?

a.){1/2, 5.5, 13 3/4, -4.5}
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b.){0, 0.9, 43/3, -2}

c.){-13.76, -5/2, 9/0, 95}

d.){2 1/2, -7, 0.2323, 0/3}