1.Buffalo herd,which once thrived in the Great Plains of North America,trampled vegetation,but this aided future plant growth and nutrients were returned.
" but this aided future plant growth and nutrients were returned."这句话错误的原因是不是因为this不能指代前面那件事（这里的this无适合名词可指代）,对吗 应该改为“this action” ,对吗?---------用THAT替换THIS,THAT------指代上面提到的内容.
2.
a.In the novel,Jane Eyre must HAVE MADE difficult choices,including forcing herself to leave the house of Mr.Rochester,the married man she love.-------谈起过去的事情就是：MUST+HAVE+过去分词 （也就是：MUST+完成式）
b.Every year,toy manufacturers gather groups of children into playrooms,
observing their choices of toys and predicting which new products will become
the most popular.
a句中的“including”修饰宾语“choice”,而b句中的“observing"修饰主语“manufacturers”,两个句子结构相同,为什么句中的doing一个修饰宾语,一个修饰主语呢?
A 中的INCLUDING- - - - 是动名词,是宾语,是CHOICES之一.
B中的PREDICTING是分词结构,等于AND PREDICT-- - - -