estimates

首先，第一句是个复合句，but连接前后两个完整的句子，表达一种转折的语意。前面一个分句的主语是estimates，谓语是indicate，宾语是一个that引导的宾语从句；后面一个分局，rates （of addition to the aquifer）是主语，are（be动词）作系动词，后面的minimal是表语，under the semiarid climatic conditions that presently exist in the region和amounting to about half a centimeter a year都是状语，unfortunately也是状语

其次，第二句根据语意，an environment that varies from place to place supports more kinds of organisms than an environment that is uniform是补充解释前面the environment的状语，主句在前面。many eclolgists是主语，think是谓语，后面又是一个that引导的宾语从句

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标签：estimates