Question 57·Hard·Boundaries
Geologists sometimes refer to diamonds as _____ minuscule inclusions—some as small as a grain of sand—frozen inside the crystals.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation questions involving a blank between two parts of a sentence, first test whether the words before and after the blank are independent clauses (full sentences) or phrases. Then identify the logical relationship: are you adding a second complete idea, giving a reason, or explaining/defining something just mentioned? Use that analysis to rule out choices that require two full clauses (like semicolons or comma + conjunction) or that introduce the wrong relationship (like "because" for cause). Finally, choose punctuation that correctly connects the structure and meaning—often a colon when a complete sentence is followed by an explanation or example.
Hints
Check if the first part is a complete sentence
Read only up to the blank: "Geologists sometimes refer to diamonds as time capsules ____." Does this part already form a complete sentence?
Look at what comes after the blank
Is "minuscule inclusions—some as small as a grain of sand—frozen inside the crystals" a full sentence with its own main verb, or is it more like a description or explanation?
Think about the relationship between the two parts
Is the second part giving a reason, adding an equal idea, or explaining what "time capsules" means? Different punctuation and connectors are used for each of these relationships.
Match the relationship to the correct punctuation
Once you decide whether the second part is a separate sentence, a reason, or an explanation of the first part, choose the option whose punctuation is used for that specific relationship.
Step-by-step Explanation
Identify the structure before and after the blank
Read up to the blank: "Geologists sometimes refer to diamonds as _____ minuscule inclusions—some as small as a grain of sand—frozen inside the crystals."
The part before the blank, "Geologists sometimes refer to diamonds as time capsules," is a complete sentence (it has a subject, verb, and expresses a full idea). The part after the blank, "minuscule inclusions—some as small as a grain of sand—frozen inside the crystals," is a description or explanation, not a full sentence (there is no main verb like "are").
Decide the relationship between the two parts
Ask what the second part is doing. It is telling us what makes diamonds "time capsules": they contain tiny inclusions. So the second part is an explanation or restatement of "time capsules," not a new, separate sentence.
We therefore need punctuation that can follow a complete sentence and introduce an explanation or elaboration, even if the words after it are not a full sentence.
Eliminate choices that require a full clause after them
A semicolon generally joins two complete sentences. Here, the words after the blank are not a complete sentence, so any punctuation that requires a full clause after it is wrong. Also, joining with a coordinating conjunction like "and" normally links two equal parts (often two full clauses or parallel structures), which we do not have.
We must choose the option that correctly introduces an explanatory phrase after a complete clause.
Select the punctuation that introduces an explanation
The only choice that correctly follows a complete sentence and introduces an explanation or restatement is the colon. So the sentence should read:
"Geologists sometimes refer to diamonds as time capsules: minuscule inclusions—some as small as a grain of sand—frozen inside the crystals."
Thus, the correct answer is time capsules:.