听力原文： Mike Leavitt, the US Secretary for Health and Human Services says surveillance and information exchange are essential in fighting the lethal H5N1 bird flu virus that has killed 60 people in four Asian countries since late 2003.
"Surveillance is very clearly our first line of defense, but it only works if there is transparency, if there is timely sharing of information, and if there is a spirit of cooperation," he said.
Mr. Leavitt made the remarks on Monday in Jakarta, having previously visited Thailand, Cambodia, Laos, and Vietnam, along with Indonesia the countries most seriously affected by bird flu.
While most of the people who have contracted the disease have caught it from close contact with infected poultry, scientists are concerned the disease may change to one easily passed between people, causing a pandemic that could kill millions.
Mr. Leavitt says the H5N1 virus has the potential to affect the world economically, socially, and politically.
"The world is a biologically dangerous place right now. Avian influenza is spreading to other nations and to other continents. An outbreak anywhere means that there is risk everywhere," added Mr. Leavitt. "No nation can afford to ignore this. The effects of a pandemic go well beyond personal health. They affect economics, they affect polities, they affect social issues, and social concerns."
Secretary Leavitt stressed ______ in the process of fighting HSN1 bird flu virus.

A. research and development of new medicine
B. new devices of prevention
C. separation of infectors
D. surveillance and information exchange