Question 144·Hard·Boundaries
Scientists recently discovered microbial communities thriving inside Antarctic rocks, an environment once considered too extreme for ____ These findings suggest that similar microbes could exist on Mars, where surface conditions are comparable.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundary questions, first check whether the text after the blank is an independent clause. If it is, decide whether the sentence should end at the blank (often signaled by a capital letter following the blank). Eliminate comma splices (comma alone) and options that would require different capitalization or additional punctuation to be correct.
Hints
Check whether the second part is a complete sentence
Look at the words after the blank: do they have a subject and a verb (something doing something)?
Decide whether you’re starting a new sentence
If the words after the blank can stand alone, consider whether the blank should end the first sentence.
Use the capital letter as a clue
The word after the blank is capitalized. What punctuation most commonly comes right before a capitalized word that is not a name?
Eliminate comma splice answers
If both sides can be complete sentences, a comma by itself is not enough to join them.
Step-by-step Explanation
Identify what comes before and after the blank
Read the text in two parts:
- Before the blank: "Scientists recently discovered microbial communities thriving inside Antarctic rocks, an environment once considered too extreme for".
- After the blank: "These findings suggest that similar microbes could exist on Mars, where surface conditions are comparable."
The words after the blank form a complete sentence (subject: "These findings"; verb: "suggest"). The words before the blank become a complete sentence once the missing word "life" is supplied.
Determine what boundary is needed
With "life" supplied, the first part is an independent clause, and the second part is also an independent clause. Two independent clauses can be separated by:
- a period, or
- a semicolon, or
- a comma plus a coordinating conjunction.
A comma alone would create a comma splice.
Use the capitalization after the blank as a clue
The word after the blank is "These" with a capital letter, which strongly signals the start of a new sentence (it is not a proper noun). That points to end punctuation before it.
Test each option
- life, creates a comma splice and does not fit the capitalization of "These."
- life; would keep the clauses in a single sentence, but standard English convention is not to capitalize the first word after a semicolon unless it is a proper noun.
- life and does not correctly join two independent clauses here (it would typically require a comma before the conjunction and a lowercase "these").
- life. correctly ends the first sentence and allows the next to begin with "These".
Therefore, the correct answer is life.