Question 166·Easy·Boundaries
When the Moon passes directly between Earth and the Sun, it casts a narrow shadow on the planet's _____ known as a total solar eclipse.
Which choice completes the text so that it conforms to the conventions of Standard English?
On boundaries questions, first determine whether the text after the blank is a complete clause or just a phrase. If it is a nonessential appositive or explanatory phrase, a comma is often the correct choice, while semicolons are reserved for joining complete clauses.
Hints
Check what comes after the blank
The words after the blank begin with "a phenomenon," which is a noun phrase, not a complete sentence.
Look for an appositive
Ask whether the words after the blank rename or explain the event described just before the blank.
Match the punctuation to the structure
If the text after the blank is extra explanatory information rather than a full clause, it needs lighter punctuation than a semicolon.
Step-by-step Explanation
Identify the complete sentence before the appositive
"When the Moon passes directly between Earth and the Sun, it casts a narrow shadow on the planet's surface" is already a complete thought.
Identify the phrase after the blank
"A phenomenon known as a total solar eclipse" is a noun phrase that renames the event just described. It is not an independent clause because it does not contain a full subject-verb structure.
Choose the punctuation that fits an appositive
Because the phrase after the blank is explanatory and nonessential, a comma is the correct boundary.
Eliminate the other options
A semicolon requires a complete clause on both sides, a colon is too strong for this appositive phrase, and no punctuation incorrectly runs the explanatory phrase into the sentence.