Answer

The correct choice:

3-4-1-2.

You need to book a ticket before travel. You can do it at home few months before travel. If you change your plans you cannot cancel the ticket. So you must be careful.

This paragraph is about booking a ticket for an airplane flight. In this case you need to understand the cause-and-effect relationship between the sentences. What do I need? You need to book a flight. How can I do this? You can do this from your home. In addition, please be advised that you cannot cancel your reservation. Conclude that you need to proceed carefully.