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 potentially deadly new strain of flu virus, A (H5N1), has appeared in 2003, again in Hong Kong. Scientists paid great attention to this virus for two reasons. First, A (H5N1) represents a novel combination of H and N spikes, the sort of new combination that has in the past been associated with major flu epidemics. Second, unlike all previous instances of new flu strains, A (H5N1) passed to humans directly from birds, in this case chickens. Fortunately the bird flu virus does not appear to spread easily from person to person.