1、which前面有逗号，逗号前面是个名词，which就近指代那个名词。Tankfield emailed Pea some photos, which did not cheer Pea up.which就近指代photos，定语从句中谓语动词did not cheer (Pea up)的发出者即从句主语即先行词photos，是photos没让豌豆家属高兴起来。
2、Tankfield emailed Pea some photos, which Pea did not find interesting.which就近指代photos，photos是定语从句中的宾语，把定语从句还原成一个完整句就是Pea did not find the photos interesting。
3、可以看到，上面两个句子都可以以that为关系代词改写，即Tankfield emailed Pea some photos that did not cheer Pea up.)Tankfield emailed Pea some photos that Pea did not find interesting.改写与原版区别在哪儿，就在一个逗号。which前面是名词，名词和which之间没逗号的，在GMAT语法里算错。