C. 2/7
Step-by-step explanation:
When two pink marbles are taken without replacement then the total number of marbles in the bag are reduced to 21 marbles. So the blue marble, which are currently in total 6 marbles, is taken out of the total of 21 marbles. The calculation of which is done as below:
Probability of Next Marble to be blue
= Blue Marble / Total Marbles in the bag
= 6 / 21
= 2 / 7
Hence, the correct option is C. 2/7