While global temperatures have risen sharply over the last century, th

While global temperatures have risen sharply over the last century, they have only recently eclipsed the Medieval period, during which scientists theorize that a series of volcanic eruptions sent the earth into a period of historic warmth.

A. they have only recently eclipsed the Medieval period, during which scientists theorize that a- comparison issue -temperatures have eclipsed the Medieval period
B. they have only recently eclipsed those of the Medieval period, during which scientists theorize that a
C. it has only recently eclipsed the Medieval period, during which, scientists theorize, a- singular pronoun 'it' tries to refer to plural noun temperatures
D. it has only recently eclipsed that of the Medieval period, during which scientists theorize a- singular pronoun 'it' tries to refer to plural noun temperatures; comparison issue -temperatures have eclipsed that of Medieval period, but 'that' can't refer to temperatures(plural)
E. they have only recently eclipsed those of the Medieval period, during which, scientists theorize, a

I was down to options B and E.
Although I chose option B, I understand that it sounds illogical because option B means that the act of theorizing was done during the Medieval period.
1. But shouldn't verbs such as theorize be followed by 'that'?
2. In OA(E), is the phrase 'scientists theorize' a non-essential phrase enclosed by commas? So, the sentence is read as 'Medieval period, during which a series of volcanic eruptions sent the Earth into a period of historic warmth.'?

AjiteshArun , GMATNinja , MagooshExpert , GMATGuruNY , VeritasPrepBrian , MartyTargetTestPrep , DmitryFarber , VeritasKarishma , generis , EducationAisle , VeritasPrepErika , other experts - please enlighten

Once we confirm #2 (you're right!) and cross off B, maybe we can see why we don't want "that."

So yes, E is saying "during which a series of eruptions . . . ," and "scientists theorize" is just an adverbial modifier telling us that all this is according to their theory. If we look at B, we can see that the meaning is quite different: "the Medieval period, during which scientists theorize." "During which" modifies the preceding noun, so we're saying that these scientists theorize during the Medieval period. They must be time travelers!

Accordingly, if we said "theorize that" in E, we'd be trying to create the same problem as in B, except that with all the commas we'd simply have an ungrammatical jumble on our hands. Contrast these two:

In summer, she said that she was hungry all the time. (Meaning: She said that she was hungry all the time. When did she say this? In summer.)
In summer, she said, the tourists crowd the beaches. (Meaning: In summer, the tourists crowd the beaches. How do I know? She said so, at some time or another.)

Dissecting the correct choice


While
global temperatures -- noun
have risen sharply --verb parallel to 'have only recently eclipsed'
over the last century,
they -- plural pronoun referring global temperatures
have only recently eclipsed -- verb
those -- pronoun referring to pronoun/temperatures
of the Medieval period,
during which, -- modifies medieval period
scientists theorize,
a series of volcanic eruptions
sent -- verb
the earth into a period of historic warmth.

While global temperatures have risen sharply over the last century, they have only recently eclipsed the Medieval period, during which scientists theorize that a series of volcanic eruptions sent the earth into a period of historic warmth.

A. they have only recently eclipsed the Medieval period, during which scientists theorize that a
B. they have only recently eclipsed those of the Medieval period, during which scientists theorize that a
C. it has only recently eclipsed the Medieval period, during which, scientists theorize, a
D. it has only recently eclipsed that of the Medieval period, during which scientists theorize a
E. they have only recently eclipsed those of the Medieval period, during which, scientists theorize, a

Subject-Verb Agreement: While looking at the answer choices, we have a 2v3 split (it has vs they have). Considering the subject of the sentence (global temperatures) is plural, the corresponding pronoun must also be plural i.e. they have. This helps in eliminating options C and D.

Logical Comparison: In option A, there is an incorrect comparison between temperatures and the Medieval period. The intended meaning of the sentence is to compare the temperatures in two different periods.

This leaves us with options B and E.

Tense/meaning: Both options use the verb 'theorise' in its present tense. However, while interpreting the meaning of the sentence in Option B, the Medieval period (which was obviously in the past) does not correspond to the present tense 'theorise'.

Option E, by using the right punctuation, gives the intended meaning of the sentence - that scientists currently theorise about the events during the Medieval Period. Ans E.