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 hollow iron pipe is 21 cm long and its external diameter is 8 cm . if the thickness of the pipe is 1 cm and iron weights 8 g / cm cube , then find the weight of the pipe . 
Options: ['a ) 3.696 kg', 'b ) 3.686 kg', 'c ) 2.696 kg', 'd ) 2.686 kg', 'e ) none of these']
Example Output: a

Example Input: Problem: a train is 360 meter long is running at a speed of 30 km / hour . in what time will it pass a bridge of 140 meter length ? 
Options: a ) 87 , b ) 69 , c ) 60 , d ) 72 , e ) 21
Example Output: c

Example Input: Problem: during a car trip , maria stopped to rest after she traveled 1 / 2 of the total distance to her destination . she stopped again after she traveled 1 / 4 of the distance remaining between her first stop and her destination , and then she drove the remaining 180 miles to her detination . what was the total distance , in miles from maria ' s starting point to her destination ? 
Options: a ) 280 , b ) 320 , c ) 360 , d ) 420 , e ) 480
Example Output:
e