Question 217·Easy·Boundaries
Researchers are exploring alternative energy sources _____ solar, wind, and geothermal power to reduce reliance on fossil fuels.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation questions involving phrases like "such as," first identify the grammatical role of the words before and after the blank: are you introducing examples, adding an interruption, or ending a complete thought before a list? Remember that "such as" normally connects directly to its examples without extra punctuation. Check colon and dash rules in particular: both require a complete sentence before them and signal a strong break, so if the text before the blank isn’t a full thought, eliminate those options quickly. Then choose the smoothest, simplest version that follows standard punctuation rules.
Hints
Clarify the structure around the blank
Focus on how "solar, wind, and geothermal power" relate to "alternative energy sources." What is the blank doing between those parts of the sentence?
Think about how examples are introduced
The words right before the blank are "energy sources" and right after the blank is a list. You are choosing how to connect "energy sources" to that list of examples.
Consider whether punctuation is needed
Ask yourself: Do we need any punctuation between the phrase that introduces examples and the examples themselves? Would adding a comma, dash, or colon there make the sentence smoother or more awkward?
Recall rules for colon and dash
A colon or dash usually follows a complete sentence and signals a strong break. Check whether the words before the blank form a complete sentence by themselves.
Step-by-step Explanation
Identify what comes after the blank
Read the full sentence with a placeholder: "Researchers are exploring alternative energy sources ___ solar, wind, and geothermal power to reduce reliance on fossil fuels."
The words after the blank—"solar, wind, and geothermal power"—are examples of the "alternative energy sources." So the blank must smoothly introduce a list of examples within the sentence.
Understand the role of "such as"
The phrase "such as" is used to introduce examples. In a sentence like this, it connects directly to the examples:
- "energy sources such as solar, wind, and geothermal power"
Here, the entire phrase functions as one unit: "sources such as solar, wind, and geothermal power." We typically do not split "such as" from its examples with punctuation unless there is some extra interruption or nonessential information.
Apply punctuation rules for commas, dashes, and colons
Now think about each punctuation mark:
- A comma right after "such as" would separate "such as" from the examples it introduces, breaking the phrase awkwardly.
- An em dash (—) signals a strong break in the sentence; it is used to set off added or interrupting information, not to separate a phrase from its own examples.
- A colon (:) must follow a complete sentence (an independent clause). The words before the blank ("Researchers are exploring alternative energy sources such as") do not form a complete thought, so a colon there would be grammatically incorrect.
So any option that adds a comma, dash, or colon after "such as" creates a punctuation error.
Choose the option that matches correct standard usage
Because the examples need to follow "such as" directly—without being separated by unnecessary punctuation—the only choice that keeps the phrase intact and follows the rules for commas, dashes, and colons is A) such as.