natural declining rate

例句：

1. 1. The company'ssales have been declining steadily sincethe beginning of the year.
   自年初以来，该公司的销售额一直在稳步下降。
2. 2. The populationis naturally declining due to agingand migration.
   由于老龄化和迁移，人口自然下降。
3. 3. The researchers found that the natural declining rate of the disease was notsignificant.
   研究人员发现，该疾病的自然下降率并不显著。