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Difficulty: MediumClause Boundaries and Linking

In volcanology, the viscosity of magma is a primary factor determining the explosiveness of an eruption. Low-viscosity basaltic magma allows trapped gases to escape relatively easily, resulting in gentle, effusive lava flows. High-viscosity rhyolitic magma, conversely, prevents these gases from escaping freely ______ pressure builds up within the volcanic chamber until it releases in a catastrophic explosion.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. A
    , consequently,
  2. B
    although
  3. ; consequently,Answer
  4. D
    consequently

Answer

The semicolon followed by the conjunctive adverb and a comma ('; consequently,') correctly links the two independent clauses.
The correct option is '; consequently,'. The sentence contains two independent clauses: the first describes how rhyolitic magma prevents gas from escaping, and the second explains that pressure builds up inside the volcanic chamber. A semicolon is required to separate these two independent clauses, and the conjunctive adverb 'consequently' followed by a comma correctly establishes the cause-and-effect relationship between the two clauses.

Step-by-Step Solution

1
Identify the clause boundaries in the sentence.
The sentence is composed of two independent clauses: 'High-viscosity rhyolitic magma, conversely, prevents these gases from escaping freely' and 'pressure builds up within the volcanic chamber until it releases in a catastrophic explosion.'
Determining if the clauses are independent or dependent tells us what punctuation or conjunctions are grammatically permissible to link them.
2
Determine the logical relationship between the two clauses.
The second clause (pressure building up) is a direct consequence of the first clause (gases being prevented from escaping). Therefore, a transition indicating cause-and-effect is needed.
This helps select the correct adverbial transition or coordinating conjunction.
3
Evaluate the grammar and punctuation of each choice.
A semicolon followed by a conjunctive adverb ('consequently') and a comma is grammatically correct for linking two independent clauses. A comma alone creates a comma splice, omitting punctuation creates a run-on, and using 'although' is logical nonsense since the relationship is causal, not concessive.
This rules out grammatically incorrect and semantically inappropriate choices to find the single correct answer.

Key Concept

Clause Boundaries and Linking
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Topics

Clause Boundaries and Linking

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