Question

Difficulty: Very hardSubject-Modifier Agreement

Complete the text by filling in the blank with the appropriate subject pronoun or noun phrase that conforms to the conventions of Standard English subject-modifier agreement.

Answer:In 1928, Paul Dirac formulated a relativistic wave equation to describe the behavior of the electron. Though initially dismissed by contemporary physicists as a mathematical curiosity with no physical relevance, 【the Dirac equation】 is now recognized as a foundational equation in quantum mechanics.

Answer

The blank must be filled with a noun phrase or pronoun that refers directly to the equation (such as 'the Dirac equation', 'this equation', or 'it') to ensure it agrees with the introductory modifying phrase 'Though initially dismissed by contemporary physicists as a mathematical curiosity with no physical relevance.'
The introductory modifying phrase 'Though initially dismissed by contemporary physicists as a mathematical curiosity with no physical relevance' must logically describe the subject that immediately follows it. In this context, the entity that was dismissed as a mathematical curiosity is the relativistic wave equation. Therefore, the blank must be filled with a noun phrase or pronoun referring to the equation (such as 'the Dirac equation' or 'it') to establish correct subject-modifier agreement.

Step-by-Step Solution

1
Identify the introductory modifying phrase and determine what it logically describes.
The modifying phrase is 'Though initially dismissed by contemporary physicists as a mathematical curiosity with no physical relevance.' The entity that was dismissed as a 'mathematical curiosity' is the relativistic wave equation formulated by Paul Dirac, not Paul Dirac himself or the contemporary physicists.
According to the rules of subject-modifier agreement, the subject of the main clause must immediately follow the introductory modifier and must be the entity that is logically described by that modifier.
2
Select a subject noun phrase or pronoun that refers to the equation to fill the blank.
Noun phrases like 'the Dirac equation', 'this equation', or the pronoun 'it' correctly identify the equation as the subject of the main clause.
This alignment prevents a dangling modifier and ensures that the sentence is grammatically correct and coherent.

Key Concept

Subject-Modifier Agreement
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