Task: Question Answering
Input (English): Problem: a sprinter starts running on a circular path of radius r metres . her average speed ( in metres / minute ) is π r during the first 30 seconds , π r / 2 during next one minute , π r / 4 during next 2 minutes , π r / 8 during next 4 minutes , and so on . what is the ratio of the time taken for the nth round to that for the previous round ? 
Options: a ) 4 , b ) 8 , c ) 16 , d ) 32 , e ) 36
Output (English): c