Task: Question Answering
Input (English): Problem: the population of locusts in a certain swarm doubles every two hours . if 4 hours ago there were 1000 locusts in the swarm , in approximately how many hours will the swarm population exceed 128000 locusts ? 
Options: a ) 12 , b ) 8 , c ) 4 , d ) 10 , e ) 16
Output (English): d