release to birth ratio

例句：

1. 1. The release to birth ratio is an important factor in determining the success of a vaccine.
   释放至出生比率是决定疫苗成功与否的重要因素。
2. 2. The study found that the release to birth ratio was higher in urban areas than in rural areas.
   研究发现，城市地区的释放至出生比率高于农村地区。
3. 3. The government is working on improving the release to birth ratio to reduce infant mortality rates.
   政府正在努力提高释放至出生比率，以降低婴儿死亡率。