1.For many revisionist historians, Christopher Columbus has come to personify devastation and enslavement in the name of progress that has decimated native peoples of the Western Hemisphere.

A. devastation and enslavement in the name of progress that has decimated native peoples of the Western Hemisphere
B. devastation and enslavement in the name of progress by which native peoples of the Western Hemisphere decimated
C. devastating and enslaving in the name of progress those native peoples of the Western Hemisphere which in the name of progress are decimated.
D. devastating and enslaving those native peoples of the western Hemisphere which in the name of progress are decimated.
E. the devastation and enslavement in the name of progress that have decimated the native peoples of the Western Hemisphere.

2. Because fish look through water, their eyes are very different from a mammal.
A. from a mammal
B. from a mammal's
C. from that of a mammal
D. than that of a mammal
E. than is a mammal's.

In the second sentence, the OA is B and in D "that" is not correct since it cannot refer to plural nouns. I quite agree with this.

Going back to the first sentence
OA is E.
1. In this sentence - Question 1 option E- what is the role of 'that' in this sentence and how different is it from the 'that' used in option D in sentence 2. Do they play different roles
2. In Sentence 1 option E, doesn't 'that' refer to a plural antecedent and use the verb have.

This is a bit confusing, can one of the experts please explain this?