In this task, you need to provide the correct option for a given problem on probability from the provided options.

Ex Input:
Problem: a box contains 2 red balls and 5 black balls . one by one , every ball is selected at random without replacement . what is the probability that the fourth ball selected is black ? 
Options: a ) 1 / 4 , b ) 7 / 5 , c ) 1 / 2 , d ) 5 / 8 , e ) 2 / 3

Ex Output:
b


Ex Input:
Problem: a question paper has 2 parts , a & b , each containing 10 questions . if a student has to choose 5 from part a & 10 from part b , in how many ways can he choose the questions ? 
Options: a ) 100 , b ) 120 , c ) 125 , d ) 350 , e ) 252

Ex Output:
e


Ex Input:
Problem: if 4 consecutive letters are selected at random from the english alphabet , then the probability that one of the letters is a vowel is ? 
Options: a ) 13 / 23 , b ) 16 / 23 , c ) 11 / 23 , d ) 17 / 23 , e ) 18 / 23

Ex Output:

d