A bag contains 4 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. $\frac{1}{3}$ c. $\frac{3}{14}$ D. $\frac{1}{4}$

Step 1 ：There are 4 red marbles, 3 blue marbles, and 7 green marbles in the bag.

Step 2 ：The total number of marbles in the bag is 4 (red) + 3 (blue) + 7 (green) = 14 marbles.

Step 3 ：The probability of an event is calculated by dividing the number of favorable outcomes by the total number of outcomes.

Step 4 ：In this case, the favorable outcome is selecting a blue marble, and the total number of outcomes is the total number of marbles in the bag.

Step 5 ：So, the probability of selecting a blue marble is \(\frac{3}{14}\).

Step 6 ：Final Answer: \(\boxed{C. \frac{3}{14}}\)