Dear Friends,
Here is a detailed explanation to this question-
eybrj2 wrote:
Navigators have known for thousands of years that the ocean has variable currents, but it is only in the last half century that a reasonably clear picture has emerged of the patterns and causes of ocean currents.
(A) a reasonably clear picture has emerged of the patterns and causes of ocean currents
(B) a reasonably clear picture of the patterns of ocean currents and their causes have emerged
(C) a reasonably clear picture emerged of ocean currents, their patterns and the causes of them
(D) there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them
(E) there had emerged a reasonably clear picture of the patterns of ocean currents and their causes
Concepts tested here: Subject-Verb Agreement + Pronouns + Tenses + Grammatical Construction + Awkwardness/Redundancy• The present perfect tense (marked by the use of the helping verb “has/have”) is used to describe events that concluded in the past but continue to affect the present.
• The past perfect tense (marked by the use of helping verb "had") is used when a sentence contains two actions in the past; the helping verb "had" is used with the action in the "greater past".
• The simple past tense is used to refer to actions that concluded in the past.
• Information that is permanent in nature is best conveyed through the simple present tense.
• The “comma + and” (oxford comma) construction is used to join the last element of a list of more than two other elements.
A: Correct. This answer choice correctly refers to the singular noun "picture" with the singular verb "has emerged". Further, Option A correctly uses the present participle verb "has emerged" to refer to an action that concluded in the past but continues to affect the present. Moreover, Option A avoids the tense error seen in Option D, as it uses the noun "causes" rather than the phrase "what caused them". Additionally, Option A avoids ambiguity, as it uses no pronouns. Option A also correctly uses conjunction ("and" in this case) to join two elements in a list - "patterns" and "causes". Besides, Option A is free of any awkwardness or redundancy.
B: Trap. This answer choice incorrectly refers to the singular noun "picture" with the plural verb "have emerged". Further, Option B suffers from pronoun ambiguity, as "their" can refer to either "patterns" or "ocean currents".
C: This answer choice incorrectly uses the simple past tense verb "emerged" to refer to an action that concluded in the past but continues to affect the present; remember, the present perfect tense (marked by the use of the helping verb “has/have”) is used to describe events that concluded in the past but continue to affect the present, and the simple past tense is used to refer to actions that concluded in the past. Further, Option C incorrectly uses conjunction ("and" in this case) to join the last element in a list of more than two elements with the other elements; remember, the “comma + and” (oxford comma) construction is used to join the last element of a list of more than two other elements. Additionally, Option C uses the needlessly wordy phrase "their patterns and the causes of them", leading to awkwardness and redundancy.
D: This answer choice incorrectly refers to the singular noun "picture" with the plural verb "have emerged". Further, Option D incorrectly uses the simple past tense verb "caused" to refer to information that is permanent in nature; remember, information that is permanent in nature is best conveyed through the simple present tense, and the simple past tense is used to refer to actions that concluded in the past. Additionally, Option D suffers from pronoun ambiguity, as "them" can refer to either "patterns" or "ocean currents". Besides, Option D uses the passive construction "there have emerged", leading to awkwardness and redundancy.
E: This answer choice incorrectly uses the past perfect tense verb "had emerged" to refer to an action that concluded in the past but continues to affect the present; remember, the present perfect tense (marked by the use of the helping verb “has/have”) is used to describe events that concluded in the past but continue to affect the present, and the past perfect tense (marked by the use of helping verb "had") is used when a sentence contains two actions in the past; the helping verb "had" is used with the action in the "greater past". Further, Option E suffers from pronoun ambiguity, as "their" can refer to either "patterns" or "ocean currents". Besides, Option E uses the passive construction "there had emerged", leading to awkwardness and redundancy.
Hence, A is the best answer choice.To understand the concept of "Present Perfect Tense" on GMAT, you may want to watch the following video (~2 minutes):
To understand the concept of "Past Perfect Tense" on GMAT, you may want to watch the following video (~2 minutes):
To understand the concept of "Simple Tenses" on GMAT, you may want to watch the following video (~2 minutes):
To understand the concept of "Oxford Comma" on GMAT, you may want to watch the following video (~2 minutes):
All the best!
Experts' Global Team
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17 Aug 2022, 04:19
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