Text 3 [A] We try our best to develop a vaccine. [B] The cause of the flu epidemics arising so often in Asia. [C] The general introduction of "BIRD FLU". [D] The reason of the new strain of flu arising. [E] The diseases caused by viruses threat human-beings. [F] The connections between bird and viruses are complex. ______ A vaccine directed against the bird flu virus has not been developed. Such a vaccine will not be easy to produce. Public health scientists have injected the duck virus into laboratory ferrets, often used as test animals in flue research because they develop classic respiratory symptoms. Is the duck virus enough like bird flu that the ferrets develop antibodies that protect against A (H5N1) The result will be known after months.