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Question

Difficulty: HardVerb Tense and Consistency

Read the passage about Marie Curie's pioneering scientific work. What is the correct form of the verb 'conduct' that fills the blank to maintain a logical and consistent sequence of verb tenses in the passage?

Answer:By the time Marie Curie discovered radium in 1898, she 【had conducted】 years of painstaking research on uranium rays in a poorly ventilated shed.

Answer

had conducted (or had been conducting)
The correct answer is 'had conducted' (or 'had been conducting') because the introductory clause 'By the time Marie Curie discovered radium in 1898' establishes a past reference point. The action of performing research happened prior to this discovery, which grammatically requires the past perfect tense to maintain a logical and consistent sequence of events.

Step-by-Step Solution

1
Identify the primary tense of the passage by looking at the surrounding context.
The verb 'discovered' is in the simple past tense, indicating that the reference point of the sentence is in the past.
Establishing the temporal anchor is necessary to determine the correct sequence of events.
2
Analyze the chronological relationship between the events in the sentence.
The action of performing research occurred prior to the discovery of radium in 1898, as indicated by the introductory phrase 'By the time'.
Understanding which action happened first determines if a perfect tense is required.
3
Apply the appropriate verb tense rule for an action completed before another past action.
An action that is completed before a specific point in the past requires the past perfect tense, which is formed using 'had' followed by the past participle of the verb ('conducted') or the past perfect continuous ('had been conducting').
Using the past perfect tense maintains the logical sequence of events and ensures grammatical consistency.

Key Concept

Using the past perfect tense to show an action completed before another past event.
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Topics

Verb Tense and Consistency

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