Five persone entered the lift cabin on the ground floor of an $8$ floor house. Suppose that each of them independently and with equal probability can leave the cabin at any flor beginning with the first, then the probability of all $5$ persons leaving at different floors is,
  • A$\frac{^{7}\text{P}_5}{7_5}$
  • B$\frac{7_5}{^{7}\text{P}_5}$
  • C$\frac{6}{^{6}\text{P}_5}$
  • D$\frac{^{5}\text{P}_5}{5}$
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