birthrate的复数形式怎么写？

birthrate的音标：birthrate的英式发音音标为：['bɜ:θˌreɪt]birthrate的美式发音音标为：['bɜθˌreɪt]...

The birthrate is on the decrease.人口出生率正在下降.The birthrate is on the decline.出生率在下降.The birthrate in the city has been decreasing.该市的出生率一直持续下降....

n.出生率...