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(B) for me. Time taken 01:24.

The key to solve this SC is to identify what does the seventeen year period signify here? To me, that seems to be the period between "two consecutive migrations". Let's evaluate choices on that basis:

(A) "between migrating"
"migrating" seems to be a "gerund" here and it's singular. We need to show that the period is between two migrations. Also, the gerund "migrating" is inferior to proper noun "migration". As a side note, choose the proper noun if you have a choice between the gerund and the proper noun. But not when the form is used as an adjective. Meaning decides the usage. For example, gerund form "migrating" will be correct in cases such as- "The decline in the population of the migrating birds is a grave concern". But, at the question at hand, proper noun "migrations" is preferred and correct. Thus, eliminate this answer choice.

(B) "between their migrations"
Here the proper noun "migrations" is used, and as we have discussed in (A), this is the preferred usage here. Also, the plural "their" refers to the plural "cicadas". This choice correctly shows that the 17 year period is between two consecutive migrations. Thus, this choice is correct, both meaning wise and comparison wise.

(C) "of migrating"
First, "of migrating" comes after a preposition "between". This is grammatically wrong. A preposition should be followed by a noun/pronoun.
Second, the sentence makes no sense. If you read the sentence with (C) in underlined portion, it a muddle of filth.

(D) "of their migrations"
You could apply the same "preposition is followed by a noun/pronoun" rule and reject this choice. But, if grammar is something that doesn't come to you, you can reject this choice for it sinks as (C) does. In fact, the "preposition rule" occurred to me while writing this answer. I rejected it in first go for it made no sense and was awful in comparison to (B). Sentences in SC should always "make sense". And if they don't, you can eliminate them for that reason alone even if you do not remember or know the grammar rules given that you have successfully identified that one choice that makes sense and conveys the meaning clearly.

(E) "as they migrate"
Again I can make a case here for the "preposition is followed by a noun/pronoun" rule. Here, the preposition "between" is followed by a dependent clause. And again, I can say that the sentence with choice in the underlined portion makes no sense and looks awful compared with (B).

Experts' Global Official Explanation:

Idioms + Meaning + Verb Forms

Understanding the intended meaning is key to solving this question; the intended meaning of the crucial part of this sentence is that the time elapsed between two consecutive migrations of the periodical cicadas is seventeen years.

• “interval + between” is a correct, idiomatic usage to refer to the interval of time between two events.
• “between” can only be used to refer to nouns.

A. This answer choice incorrectly uses “between” to refer to the present participle (“verb+ing - “migrating”); please remember, “between” can only be used to refer to nouns.

B. Correct. This answer choice correctly uses the idiomatic construction “interval + between” to refer to the interval of time between the migrations of the periodical cicada. Further, Option B uses the phrase “seventeen year interval between their migrations”, conveying the intended meaning-that the time elapsed between two consecutive migrations of the periodical cicadas is seventeen years. Additionally, Option B correctly uses “between” to refer to the noun “migrations”.

C. Trap. This answer choice incorrectly uses the unidiomatic construction “interval + of” rather than the idiomatic construction “interval + between” to refer to the interval of time between the periodical cicada’s migrations; please remember, “interval + between” is a correct, idiomatic usage to refer to the interval of time between two events. Further, Option C alters the meaning of the sentence through the phrase “seventeen year interval of migrating”; the construction of this phrase incorrectly implies that the periodical cicadas migrate for an interval of seventeen years; the intended meaning of the crucial part of this sentence is that the time elapsed between two consecutive migrations of the periodicalcicadas is seventeen years.

D. This answer choice incorrectly uses the unidiomatic construction “interval + of” rather than the idiomatic construction “interval + between” to refer to the interval of time between the periodical cicada’s migrations; please remember, “interval + between” is a correct, idiomatic usage to refer to the interval of time between two events.

E. Trap. This answer choice incorrectly uses the unidiomatic construction “interval + as” rather than the idiomatic construction “interval + between” to refer to the interval of time between the periodical cicada’s migrations; please remember, “interval + between” is a correct, idiomatic usage to refer to the interval of time between two events.Further, Option E alters the meaning of the sentence through the phrase “seventeen year interval as they migrate”; the construction of this phrase incorrectly implies that the cicadas live underground during the seventeen year period, during which they migrate; the intended meaning is that the cicadas live underground during the seventeen year periods between their migrations.

B is the best answer choice.

Experts' Global Video Explanation: