And where is it now

Where did the H5N1 virus come from and where is it now?

H5N1病毒从哪里的？现在分布在哪里？

The southern frontier of the desert was far to the north of where it is now, while semiarid grassland and shallow freshwater lakes covered much of what are now arid plains.

过往沙漠的南部边界比现在的边界更靠北，而半干旱的草原和较浅的淡水湖泊覆盖了现在干旱平原的大部分地区。

It has now reached a point where a growing number of people believe that it is far too high, and that bringing it down will be one of the great challenges of the twenty first century.

现在，到了越来越多人认为它太高了的程度，而且使它降低将是21世纪最大的挑战之一。