Question 17·Medium·Boundaries
The park's boardwalk zigzags for nearly two miles across the _____ visitors to observe herons, turtles, and even the occasional otter along the way.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundary questions, read the sentence with each option inserted and identify whether the words before the punctuation form an independent clause. Then identify what comes next: an independent clause (semicolon/period possible), a dependent clause (comma usually not enough by itself), or a phrase like a participial phrase (comma often appropriate). Avoid adding a conjunction like "and" unless it truly connects parallel grammatical structures.
Hints
Hint 1: Find the complete idea
Ask yourself: once you include the shared word from the options, do you have a complete sentence before the punctuation?
Hint 2: What kind of group is after the blank?
Focus on the word allowing. Does what follows it form a complete sentence, or is it a describing/modifying phrase?
Hint 3: Match punctuation to structure
A semicolon joins two complete sentences. A comma can separate a complete sentence from a following participial phrase. Which option matches that rule?
Hint 4: Think about "and"
If you include ", and allowing," what exactly is and connecting? Are those two parts grammatically parallel?
Step-by-step Explanation
Identify the complete main clause
Insert the shared word in each option to read the full main clause:
"The park's boardwalk zigzags for nearly two miles across the marsh"
This is a complete independent clause (subject: "boardwalk"; verb: "zigzags"). The next part of the sentence will either start a new clause or add a modifying phrase, so the punctuation after marsh must fit what follows.
Recognize the structure that follows
What follows the blank begins with allowing:
"allowing visitors to observe herons, turtles, and even the occasional otter along the way."
This is a participial (-ing) phrase that modifies the main clause; it is not an independent clause and cannot stand alone as a complete sentence.
Match punctuation to clause types
A semicolon can join only two independent clauses. Because "allowing visitors to observe..." is a phrase (not a full sentence), a semicolon before it is incorrect.
A comma is the standard way to set off a nonessential participial phrase that follows a complete clause.
Eliminate incorrect structures and choose the best option
- "marsh; allowing" is incorrect because the second part is not an independent clause.
- "marsh allowing" creates an unclear/misattached modifier (it can sound like the marsh is "allowing" visitors).
- "marsh, and allowing" wrongly uses and to join non-parallel structures.
Therefore, the best choice is "marsh, allowing."