In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: a cyclist rides a bicycle 8 km at an average speed of 10 km / hr and again travels 10 km at an average speed of 8 km / hr . what is the average speed for the entire trip ? 
Options: a ) 9.28 , b ) 8.48 , c ) 8.78 , d ) 8.98 , e ) 9.18
Example Output: c

Example Input: Problem: what is 2 3 / 4 - 1 2 / 5 divided by 2 / 3 - 1 / 3 ? 
Options: a ) 17 / 36 , b ) 36 / 17 , c ) 7 / 6 , d ) 27 / 20 , e ) 51 / 44
Example Output: d

Example Input: Problem: how many pairs ( r , r + 1 ) have one or more prime factors common , where r is an integer and 2 ≤ r ≤ 9 ? 
Options: a ) 0 , b ) 1 , c ) 2 , d ) 3 , e ) 4
Example Output:
a