Question 36·Hard·Boundaries
In the 1930s, geophysicist Inge ______ discovered that Earth's core has a solid inner layer beneath the molten outer core.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation questions with a name followed by a descriptive phrase (e.g., 'Marie Curie, a physicist, ...'), first decide if the description is essential. If not, treat it as a nonessential appositive and ensure it is set off by commas on both sides when it appears mid-sentence. Plug each option into the sentence and read it with and without the descriptive phrase; the correct choice will allow the sentence to read smoothly both ways and will use two commas to bracket the appositive.
Hints
Test the sentence without the middle phrase
Read the sentence ignoring 'a Danish scientist.' Does 'In the 1930s, geophysicist Inge Lehmann discovered that Earth's core has a solid inner layer...' still make sense?
Think about commas around extra information
If a phrase just adds extra information about a person already clearly named, ask whether it should be separated from the rest of the sentence with commas.
Compare where you naturally pause
Try saying each option out loud in the sentence and notice where you naturally pause around 'a Danish scientist.' The punctuation should match those pauses on both sides if the phrase is extra information.
Step-by-step Explanation
Identify the role of the phrase
Look at the sentence with the blank:
In the 1930s, geophysicist Inge ______ discovered that Earth's core has a solid inner layer beneath the molten outer core.
The phrase in the choices, 'a Danish scientist', gives extra information about who Inge Lehmann is. It renames or describes the same person, so it is an appositive (a descriptive phrase that adds more information about a noun).
Decide if the information is essential or extra
Ask: Do we need 'a Danish scientist' to know which person we are talking about?
- 'Inge Lehmann' already clearly identifies the person.
- 'a Danish scientist' is extra detail that could be removed without changing who is meant.
That makes it nonessential information, and nonessential appositives are set off with commas on both sides when they appear in the middle of a sentence (pattern: Name, extra info, rest of sentence).
Check each choice for correct comma placement
We need a version that places commas both before and after the nonessential appositive between the name and the verb:
- 'Lehmann, a Danish scientist' → only a comma before the phrase, not after it.
- 'Lehmann a Danish scientist,' → only a comma after the phrase, not before it.
- 'Lehmann a Danish scientist' → no commas at all.
- 'Lehmann, a Danish scientist,' → commas before and after the phrase, giving: 'Inge Lehmann, a Danish scientist, discovered ...', which is correct.
Therefore, the correct answer is 'Lehmann, a Danish scientist,'.