The only incorrect answer is d. Scan external files from only unverifiable sources before uploading to computer
While it is true that you should scan files before uploading them to your computer or, as a matter of fact, any device in general, it is not true that you should scan files that come only from unverifiable sources. All sources that have contact with your computer should be scanned because you can not be sure that even the most verified sources are not infected.
