isotope ratio tracer method

例句：

1. 1. The isotopes were used to trace the movement of water in the river.
   使用同位素追踪河流中水的运动。
2. 2. The scientist used the isotope ratio tracer method to study the composition of the soil.
   科学家使用同位素比值示踪法研究土壤的成分。
3. 3. The method was used to determine the isotopic ratios of the samples.
   该方法用于确定样本的同位素比值。