Question 49·Easy·Boundaries
While analyzing satellite images, researchers identified a series of unusual cloud formations, _____
Which choice completes the text so that it conforms to the conventions of Standard English?
For sentence-boundary and punctuation questions, first identify the main clause and check whether you already have a complete sentence before or after the blank. Then test each option by reading the full sentence out loud (or in your head) and watch for common errors: comma splices (two full sentences with just a comma), fragments, unnecessary commas before essential "that" clauses, and incorrect end punctuation (like question marks on clear statements). Eliminate any option that breaks these basic rules, and choose the one that preserves a single, clear, correctly punctuated sentence.
Hints
Check if you already have a complete thought
Ask yourself: does "researchers identified a series of unusual cloud formations" already form a complete statement? If so, what should the part after the comma be doing?
Decide between a phrase or a new sentence
Look at each option and ask: does this add extra information about the same idea, or does it start a new independent sentence? Remember that a comma cannot join two complete sentences by itself.
Watch punctuation and sentence type
Notice which option turns the sentence into a question with a question mark and which options end with a period. Does anything in the beginning of the sentence suggest it should be a question?
Think about commas with "that"
When a "that" clause is essential to identify or describe a noun, do we usually put a comma right before "that," or do we attach it directly to the noun?
Step-by-step Explanation
Identify the main structure of the sentence
First, read the sentence without the blank:
"While analyzing satellite images, researchers identified a series of unusual cloud formations, _____"
The core idea is that researchers identified something. The part after the comma should smoothly add information about those cloud formations without turning the sentence into a run-on or a question.
Decide what kind of phrase is needed
Because there is already a complete statement ("researchers identified a series of unusual cloud formations"), the blank should be filled with a phrase that adds detail about that discovery, not a brand-new, separate sentence. So we are looking for wording that continues the same sentence correctly after the comma.
Eliminate options that create the wrong sentence type
Check each option in the full sentence:
- If the option turns the sentence into a question, that is wrong because nothing in the beginning suggests a question.
- If the option creates two complete sentences joined only by a comma, that is a comma splice (a type of run-on) and is incorrect.
- If the commas around "that" break apart a noun from its essential description, that also breaks standard punctuation rules.
Test each option for comma and boundary errors, then choose the best
Now plug in each option:
- A) "a discovery, that prompted further investigation." puts a comma between the noun "discovery" and an essential "that" clause. In standard English, we do not separate an essential "that" clause from the noun it describes with a comma, so this is wrong.
- B) "and prompting further investigation?" adds "and" plus a participle without a clear subject, and incorrectly changes the sentence into a question, so it is ungrammatical.
- C) "this discovery prompted further investigation" creates two full sentences joined only by a comma (a comma splice): "..., researchers identified... , this discovery prompted..." That is not allowed.
- D) "a discovery that prompted further investigation." correctly continues the sentence with a single noun phrase that explains the cloud formations and uses no unnecessary comma before "that." It is grammatically correct and properly punctuated.
Therefore, the correct answer is D) a discovery that prompted further investigation.