Which sentence correctly uses a semicolon? 

1. I have a big test tomorrow; so I need to study
2. I have a big test tomorrow; I need to study
3. I have a big test tomorrow; therefore, I need to study
4. I have a big test tomorrow, I need to study

Semicolons connect independent clauses without conjunctions. Option a misuses “so” (conjunction), while option d creates a comma splice. Option c is technically correct but overly formal. MLA Handbook recommends semicolons for closely related ideas. Example: “The sky darkened; rain began.”