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Rats have been shown to engage in multiple forms of reciprocal help and cooperation, including what is referred to as direct reciprocity—where a rat will help another rat that has previously helped them.

【结构分析】

主干部分：

Rats have been shown to engage in multiple forms of reciprocal help and cooperation

修饰成分：

including……为伴随状语;

what is referred to as direct reciprocity为动名词including后的宾语从句;

where a rat will help another rat为定语从句修饰direct reciprocity;

that has previously helped them为定语从句修饰another rat;

【译文】

有研究表明，老鼠会进行多种多样形式的互助及合作，其中包括被称为直接互惠的行为，即老鼠会帮助曾经帮助过自己的另一只老鼠。