Everybody may have seen the film "Death on the Nile (n. )", but nobody can imagine that the writer of the story, Agatha Christie, saved a baby in a most unusual way. In June 1977, a baby girl became seriously ill in Deleville. Doctors there were unable to find out the cause of her illness, so she was sent to a famous hospital in London, where there were many excellent doctors. The baby was so seriously ill that a team of doctors hurried to examine the baby without delay. The doctors, too, were puzzled by the baby's illness and they also became discouraged. Just then a nurse asked to speak to them. "I think the baby is suffering from thallium (n. ) poisoning. " said the nurse. "A few days ago, I read a story 'A Pale Horse' written by Agatha Christie. Someone uses thallium poison, and all the symptoms are written in the book. They are exactly the same as the baby's." "You're very good at observing things," said a doctor, "and you may be right. We'll carry out some tests and find out whether the cause is thallium poisoning or not." The tests proved that the baby had indeed been poisoned by thallium. Once they knew the cause, the doctors were able to give her correct treatment. The baby soon got well and was sent back to Deleville A week later, it was reported that the poison might have come from an insecticide (n. ) used in Deleville. From this passage it seems that the baby's illness had something to do with    _   .
a dead writer the water in Deleville a dangerous murderer a harmful substance (n. ) used to kill pests