Read the sentences and decide which one of the given words fits each gap in the expressions:
1. After you finish, you need to log ______ .
2. You need to back ______ your important files.
3. Remember to switch this ______ when you are not using it to save power.
4. It's not enough to just delete the information. It is still there and can be recovered. You need to wipe it ______ with a special program.