Punctuate boundaries between independent clauses (period, semicolon, comma+conjunction).
Two independent clauses can be separated by a period, semicolon, or comma plus coordinating conjunction.
核心知识
Two independent clauses can be separated by a period, joined by a semicolon, or connected with a comma plus a coordinating conjunction (FANBOYS). A comma alone never works.
深入理解
When two clauses can each stand as their own sentence, you have three legal ways to handle the boundary:
Period: full separation. Each clause becomes its own sentence.
→ "The river flooded. The town evacuated."
Semicolon: signals that the two ideas are closely related.
→ "The river flooded; the town evacuated."
Comma + coordinating conjunction (for, and, nor, but, or, yet, so):
→ "The river flooded, so the town evacuated."
What never works: a comma by itself between two independent clauses. That's a comma splice.
On the SAT, the answer choices typically offer several of these options plus one illegal one (usually a comma splice or run-on). Your job is to pick whichever choice produces a grammatically complete, correctly punctuated sentence.
One subtlety: a semicolon and a period are interchangeable in terms of grammar. If both appear as options, look at the other choices—usually only one of the two is offered alongside a clearly wrong alternative.
分步讲解
- Find the boundary point—where does one clause end and the next begin?
- Confirm both clauses are independent (each has a subject and verb and expresses a complete thought).
- Check the answer choices: period, semicolon, or comma + FANBOYS are all acceptable.
- Eliminate any option that uses a comma alone between the two independent clauses.
- If multiple options seem correct, check for meaning shifts introduced by different conjunctions.
常见误解
- "A semicolon is just a fancy comma." A semicolon replaces a period—it joins two independent clauses. A comma cannot do that job alone.
- "You always need a conjunction after a comma between clauses." True for independent clauses, but dependent clauses joined to independent ones often use just a comma.
- "FANBOYS conjunctions can follow a semicolon." No—semicolons replace the comma + conjunction combination. You wouldn't write "; and" between independent clauses.
示例解析
In a 2023 study published in Nature, geneticist Dr. Kenji Tanaka demonstrated that certain deep-sea organisms can repair DNA damage far more efficiently than their shallow-water ______ other laboratories are now testing whether the same mechanism can be activated in mice.
Which choice completes the text so that it conforms to the conventions of Standard English?
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