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Here is a detailed explanation to this question-
lgon wrote:
New techniques in thermal-scanning photography, a process that records radiation from surface areas, makes it possible to study the effects of calefaction, or warming, of a river in greater detail than ever before.
(A) makes it possible to study the effects of calefaction, or warming, of a river in greater detail than ever before
(B) make it possible to study, in greater detail, the effects of calefaction, or warming, of a river than ever before
(C) have made it possible to study in greater detail than ever before the effects of calefaction, or warming, of a river
(D) make possible the study of the effects of calefaction, or warming, of a river in greater detail than it ever was before
(E) has made it more possible than ever before to study in greater detail the effects of calefaction, or warming, of a river
Meaning is crucial to solving this problem:Understanding the intended meaning is key to solving this question; the intended core meaning of the sentence is that new techniques in thermal-scanning photography have made it possible to study the effects of the calefaction of a river in greater detail than ever before.
Concepts tested here: Subject-verb Agreement + Meaning + Tenses + Verb Forms + Redundancy/Awkwardness• 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 simple present tense is used to indicate actions taking place in the current time frame, indicate habitual actions, state universal truths, and convey information that is permanent in nature.
• The infinitive verb form (“to + base form of verb"- "to + study" in this sentence) is the preferred construction for referring to the purpose/intent of an action.
A: This answer choice incorrectly uses the singular verb “makes” to refer to the plural noun “techniques”. Further, this answer choice incorrectly uses the simple present tense verb "makes" to refer to an action that happened in past but continues to affect the present; please 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 present tense is used to indicate actions taking place in the current time frame, indicate habitual actions, state universal truths, and convey information that is permanent in nature.
B: Trap. This answer choice incorrectly uses “than ever before” to modify “calefaction...of a river" rather than “in greater detail”, leading to an incoherent meaning; the intended meaning of the sentence is the new techniques in thermal-scanning photography have made it possible to study the effects of the calefaction of a river in greater detail than ever before. Further, Option B incorrectly uses the simple present tense verb "makes" to refer to an action that happened in past but continues to affect the present; please 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 present tense is used to indicate actions taking place in the current time frame, indicate habitual actions, state universal truths, and convey information that is permanent in nature.
C: Correct. This answer choice correctly uses the plural verb “have made” to refer to the plural noun “techniques. Further, Option C correctly uses “than ever before” to modify “in greater detail”, conveying the intended meaning - that the new techniques in thermal-scanning photography have made it possible to study the effects of the calefaction of a river in greater detail than ever before. Additionally, Option C correctly uses the present perfect tense verb “have made” for an action that happened in past but continues to affect the present. Option C also uses the infinitive verb form (“to + base form of verb” – “to + study” in this sentence) to refer to the intent of the action “have made it possible”. Besides, Option C is free of awkwardness and redundancy.
D: This answer choice incorrectly uses the simple present tense verb "makes" to refer to an action that happened in past but continues to affect the present; please 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 present tense is used to indicate actions taking place in the current time frame, indicate habitual actions, state universal truths, and convey information that is permanent in nature. Further, Option D uses the noun phrase “the study of the effects of calefaction” to refer to the intent of the action “make possible”; please remember, the infinitive verb form (“to + base form of verb") is the preferred construction for referring to the purpose/intent of an action. Besides, Option D uses the needlessly wordy phrase “make possible the study of the effects of calefaction”, leading to awkwardness and redundancy.
E: This answer choice incorrectly uses the singular verb “has made” to refer to the plural noun “techniques”. Additionally, the phrase “more possible than ever before to study in greater detail the effects of calefaction” is needlessly wordy, leading to awkwardness in this answer choice.
Hence, C is the best answer choice.To understand the concept of "Simple Tenses" on GMAT, you may want to watch the following video (~2 minutes):
To understand the concept of "Present Perfect Tense" on GMAT, you may want to watch the following video (~1 minute):
All the best!
Experts' Global Team