Task: Question Answering
Input (English): Problem: in a certain pond , 50 fish were caught , tagged , and returned to the pond . a few days later , 50 fish were caught again , of which 4 were found to have been tagged . if the percent of tagged fish in the second catch approximates the percent of tagged fish in the pond , what is the approximate number of fish in the pond ? 
Options: a ) 200 , b ) 325 , c ) 565 , d ) 625 , e ) 700
Output (English): d