A Bag Contains 2 Red Marbles, 3 Blue Marbles, and 7

A bag contains 2 red marbles, 3 blue marbles, and 7 green marbles. If a marble is randomly selected from the bag, what is the probability that it is blue?

A) $\frac { 1 } { 7 }$

B) $\frac { 1 } { 9 }$

C) $\frac { 1 } { 3 }$

D) $\frac { 1 } { 4 }$