Growth Factors for the Population of Atlanta in the Past $\sqrt { 15 }$

Multiple Choice

Growth factors for the population of Atlanta in the past five years have been 1, 2, 3, 4 , and 5.The geometric mean is

A) 15.
B) $\sqrt { 15 }$ .
C) $\sqrt { 120 }$ .
D) $\sqrt [ 5 ] { 120 }$ .