In 1977, a dead author of detective stories saved the life of a 19-month-old baby in a most unusual way. The author was Agatha Christie, one of the most successful writers of detective stories in the world. In June 1977, a baby girl became seriously ill in Qatar, near Saudi Arabia. Doctors were unable to find out the cause of her illness with confidence, so she was sent to Hammersmith Hospital in London. She was then only semi-conscious and on the "Dangerously Ill" list. A team of doctors hurried to examine the baby only to discover that they, too, were confused by the very unusual symptoms  . While they were discussing the baby's case, a nurse asked to speak to them. "Excuse me," said Nurse Marsha Maitlan, "but I think the baby is suffering from thallium   poisoning." "What makes you think that?" Dr. Brown asked. "Thallium poisoning is extremely rare." "A few days ago, I was reading a novel called A Pale Horse by Agatha Christie," Nurse Maitlan explained. "In the book, somebody uses thallium poison, and all the symptoms are described. They're exactly the same as the baby's." "You're very thoughtful and you may be right," another doctor said. "We'll carry out some tests and find out whether it's thallium or not." Tests showed that the baby had indeed been poisoned by thallium, a rare metallic substance used in making special glass. Once they knew the cause of the illness, the doctors were able to give the baby the correct treatment. She soon recovered and was sent back to Qatar. Later it was reported that the poison might have come from an insecticide   used in Qatar. It seems likely from the passage that the baby's illness had something to do with   _  .
a harmful substance used to kill insects a dangerous pair of glasses the water in Qatar a dead writer