Questions 11 to 13 are based on the
following passage. At the end of the conversation, you will be given 15 seconds
to answer the questions. Now listen to the
passage.
Why did John Hailor and William Liburdy, doctors in Boston, study 1,100 children
A．To examine whether these children were healthy. B．To find out whether their mothers had smoked. C．To find out why these children suffered breathing problems and lung disease. D．To look into the effect that mother’s smoking had on their children.