Identify the sentence that uses a semicolon correctly.

1. ক
   I have a big test tomorrow; I can't go out tonight.
   
2. খ
   I have a big test tomorrow; because I can't go out.
   
3. গ
   I have a big test; tomorrow, I can't go out.
   
4. ঘ
   I have a big test tomorrow; and I can't go out.