Question 197·Medium·Boundaries
In her influential 1963 lecture on space exploration, physicist L. J. Smith described humanity’s next challenge as ____ we could send a spacecraft to another planet, we could discover entirely new forms of life.
Which choice completes the text so that it conforms to the conventions of Standard English?
For SAT punctuation and boundary questions, first identify the clause before and after the punctuation: ask whether each side is a complete idea and what their relationship is (example, explanation, contrast, etc.). Then match that relationship to the standard uses of punctuation: use a colon when a complete idea is followed by an explanation or example, a semicolon between two related complete ideas, a comma for smaller breaks (not for joining two full sentences by itself), and no punctuation only when the words naturally flow together without a needed pause.
Hints
Locate the main idea before and after the blank
Read from the beginning of the sentence up to the blank, then from the blank to the period. What is being described before the blank, and what is being said after it?
Decide what the phrase after the blank is doing
Ask yourself: Is the part that begins with "if we could send a spacecraft..." giving a new, separate statement, or is it explaining what "this" (the challenge) actually means?
Match the job of the punctuation to the relationship
Think about how commas, colons, semicolons, or no punctuation are normally used between parts of a sentence. Which type is used when the second part spells out or elaborates on the first part?
Step-by-step Explanation
Understand the structure of the sentence
Read the sentence with the blank filled generically:
"... described humanity’s next challenge as ____ we could send a spacecraft to another planet, we could discover entirely new forms of life."
Notice that after the blank we get a full conditional idea: "if we could send a spacecraft to another planet, we could discover entirely new forms of life." This part explains what the “next challenge” is.
Identify the two main parts being linked
There are two key parts:
- Main statement: "physicist L. J. Smith described humanity’s next challenge as this"
- Explanation of what “this” means: "if we could send a spacecraft to another planet, we could discover entirely new forms of life."
Whatever punctuation we choose in the blank must correctly connect the word "this" to the explanatory statement that follows.
Recall how the punctuation choices function
Look at what each answer would produce at the blank:
- A) "this, if we could send..."
- B) "this: if we could send..."
- C) "this; if we could send..."
- D) "this if we could send..."
Ask: Which punctuation best signals that what follows is a detailed explanation of “this challenge,” and also creates a clear, grammatically correct connection between the parts?
Choose the punctuation that clearly introduces an explanation
The phrase before the blank ("described humanity’s next challenge as this") is a complete idea that sets up an explanation of what "this" means. Standard English conventions call for a colon to introduce that explanation, so the correct completion is "this: if".