Final answer:
The most common method of distributing malware among the choices offered is drive-by downloads. This technique infects devices by downloading malware without consent when a user visits a compromised webpage, requiring minimal interaction from the user.
Step-by-step explanation:
Of the choices listed for malware distribution methods, the most common is A. Drive-by downloads. This technique involves downloading malicious software to a user's device without their consent, often when they visit a compromised website. It's a prevalent method used by attackers because it can be deployed to a large number of users quickly and requires minimal interaction from the victims. Unlike USB flash drives, which require physical access and user interaction, or ransomware and unapproved software, which are types of malware rather than distribution methods, drive-by downloads can infect a device merely through web browsing.