options: f : i see . it 's 2:30 now , f : ok. i know . you just end using the computer at 4:00 . f : ok. i know . you just start using the computer at 4:00 . f : what ? lucy started using the computer at 4:30 .
article: f : david , it 's already 4:30. you 've been in front of the computer for 2 hours . m : no , i have n't . i just got here half an hour ago . f : then , who was using the computer before ? m : lucy .