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

Example Input: Problem: a train 300 m long takes 9 sec to cross a man walking at 3 kmph in a direction opposite to that of the train . find the speed of the train ? 
Options: a ) 100 kmph , b ) 90 kmph , c ) 120 kmph , d ) 117 kmph , e ) 125 kmph
Example Output: d

Example Input: Problem: a man cycling along the road noticed that every 18 minutes a bus overtakes him and every 6 minutes he meets an oncoming bus . if all buses and the cyclist move at a constant speed , what is the time interval between consecutive buses ? 
Options: a ) 5 minutes , b ) 6 minutes , c ) 8 minutes , d ) 9 minutes , e ) 10 minutes
Example Output: d

Example Input: Problem: points a , b , c , and d , in that order , lie on a line . if ab = 2 cm , ac = 5 cm , and bd = 9 cm , what is cd , in centimeters ? 
Options: a ) 1 , b ) 2 , c ) 3 , d ) 6 , e ) 5
Example Output:
d