Questions 17—20 are based on the following talk．You now have 20 seconds to read Questions 17～20．

For what purpose were those five hundred critically ill patients investigated（）

A．Observing how they reacted to the crisis of death．
B．Helping them and their families overcome the fear of death．
C．Finding out their attitude towards the approach of death．
D．Learning how to best help them and their families．