One dash in, one comma out: the SAT's mismatched-pair trap
"The rover — launched in 2003, transmitted for six years." One dash, one comma. The SAT writes this choice on purpose.
Why it happens
Each punctuation mark looks individually defensible, so you evaluate them one at a time and both pass. The error only exists in the relationship between them, which is exactly the thing a left-to-right read never checks.
See the trap
"The rover ___ launched in 2003 ___ transmitted data for six years."
✗ The trap: "rover — launched in 2003, transmitted" — a dash opened it and a comma closed it.
✓ The fix: "rover, launched in 2003, transmitted" — two commas. Two dashes would also be correct; one of each never is.
How to actually fix it
- Find the interrupting phrase and mark both of its edges.
- Check that the two marks are the same kind — comma/comma, dash/dash, or parenthesis/parenthesis.
- Delete the phrase and read what is left. It should still be a complete sentence.
Made this mistake on a real question?
Practice Standard English Conventions questions here. Miss one and it is logged with the exact error, then brought back until you beat it.
Practice Standard English Conventions →FAQ
Are the three pairs interchangeable?
For SAT purposes, structurally yes — they differ only in emphasis. The test will offer just one matched pair among the choices, so matching is what you check.
How do I stop repeating this mistake?
Reading the explanation isn't enough — your brain needs to beat the trap on a fresh question. Practice the skill in the kaoshen.co question bank: miss one and it is logged with the exact error, then brought back to you three days later and again after fourteen.