The medieval scholar made almost no attempt to investigate

nor can be used with "not" also.
1)not/neither X nor Y.
2)not/neither X or Y or ......nor Z.

Please correct, if above wrong.

+1 D, First it logical parallelism between the nouns, & they clearly refer to plants

Main Issues:

1) Idiom: "Neither...nor" is used in a pair for a list of 2 items. Otherwise, we use "or" for a longer list.
2) Meaning: "one another" reflects the correct meaning. Other idioms such as "next" and "some other" distort meaning here.
3) Modifier: "where" is only used to modify places. Hence, it can't be used to modify "ways".
4) Verb: Need present here to show a fact

(A) nor the ways where each was related to the other - Wrong
(B) nor how each was related to some other - Wrong
(C) or the way where one is related to the next - Wrong
(D) or the ways in which they are related to one another - Correct
(E) or the ways that each related to some other - Wrong

first, we don't have "not" nor "neither" before the underlined part. Therefore, we cannot use "nor". A and B are out.

"where" is wrong because "the ways" is not actually a place. C out. In addition, "one" and "next" are not consistent. "one" should parallel to "one" etc.

Notice that in D, we use "one another" which is actually plural just like "each other" (plural as well), and "others". We have to use a plural subject. For example. All the students like each other. Here, "all the students" is plural, and that is why "each other" makes sense here. The same logic applies to "one another" as well.

In E, "each" singular is not consistent with "some other". If we want to use "some other", we have to follow it by some nouns: "some other people", "some other books". Or, we have to say "some others". We cannot use "some other" alone.

My two cents on the correct answer

The sentence does not draw a comparison but lists the items that were not compared by medieval scholar, so this rules out A, B easily

(C) or the way where one is related to the next - next is used for sequence, but we are not concerned with any sequence here, so rule this out
(D) or the ways in which they are related to one another - After POE, we are left with this and this fits nicely, hence the correct answer
(E) or the ways that each related to some other - original meaning of sentence implies that the items are related to one another, so some other is illogical

In this context plants(general defenition) sounds like 3 or more, thus one another must be used.

For two things= use each other

For 3 or more= use one another

Plus where is supposed to modify noun places, which the word ways is not.

In which is the correct pronoun to modify the word WAYS!

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