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

Example Input: Problem: a question paper has 2 parts , a & b , each containing 5 questions . if a student has to choose 3 from part a & 4 from part b , in how many ways can he choose the questions ? 
Options: a ) 50 , b ) 100 , c ) 152 , d ) 150 , e ) 55
Example Output: a

Example Input: Problem: how many different ways can 2 students be seated in a row of 6 desks , so that there is always at least one empty desk between the students ? 
Options: a ) 2 , b ) 3 , c ) 4 , d ) 20 , e ) 12
Example Output: d

Example Input: Problem: what is the probability of randomly selecting one of the shortest diagonals from all the diagonals of a regular hexagon ? 
Options: a ) 1 / 4 , b ) 1 / 3 , c ) 1 / 2 , d ) 2 / 3 , e ) 7 / 9
Example Output:
d