You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[Q]: Question: x% of y is y% of ?

 Option A: x

 Option B: 100x

 Option C: x/100

 Option D: y/100

 Option E: None
[A]: Option A


[Q]: Question: A coin is tossed two times. What is the probability that there is at the least one tail?

 Option A: 3/4

 Option B: 31/37

 Option C: 31/18

 Option D: 31/10

 Option E: 31/19
[A]: Option A


[Q]: Question: A bag has 9 green balls and 23 pink balls. How many green balls should be added to the bag so that the ratio of green balls and pink balls in the bag becomes 1:1?

 Option A: 10

 Option B: 11

 Option C: 12

 Option D: 13

 Option E: 14
[A]:
Option E