Which is correct system sequence diagram?

Related questions

1. How are the diagrams divided in UML?
2. What is Swimlane diagram in UML?
3. What is illustrated in a UML Sequence Diagram?
4. What is ref in sequence diagram?
5. What are types of UML diagrams?
6. What is difference between sequence diagram and collaboration diagram?
7. Is flowchart a UML diagram?
8. What is ALT in sequence diagram?
9. What is the use of system sequence diagram?
10. Why is sequence diagram used?

Tags

1. #particular
2. #external
3. #system
4. #engineering
5. #possible
6. #shows
7. #actors
8. #generate
9. #their
10. #scenario
11. #events
12. #diagram
13. #sequence
14. #software
15. #inter
16. #order