问题详情

Precipitation that falls at Sites 1, 2, and 3 soaks into the soil until it reaches the groundwater table about 3 m below the surface. Based on Figure 3, and assuming no alteration of the precipitation, the δ18O value of present-day precipitation in the study area is closest to:
A.-26.
B.-23.
C.-20.
D.-15.请帮忙给出正确答案和分析，谢谢！