Five persons entered the lift cabin on the grounq floor of an 8-floor house . Suppose that each of them independently and with equal probability can leave the cabin at any floor beginning with the first. The probability of all five persons leaving at different floors , is

Options

A. a)`^7C_5/7^5`
B. b) `^7C_5 *5!/5^7`
C. c) `^7C_5 * 5!/7^5`
D. d) `5!/7^5`