Final answer:
The answer to the security threat that requires the attacker to be in physical proximity to the target is shoulder surfing. This practice involves observing someone's private information by looking over their shoulder while it's entered on a device.
Step-by-step explanation:
The security threat that requires the attacker to be physically located near the target machine is A. Shoulder surfing. Shoulder surfing involves directly observing someone's personal information as they enter it on a device, such as looking over someone's shoulder to get their ATM pin or password. This act requires the attacker to be in close proximity to the victim to see the credentials being entered.
Other options like social engineering and phishing can often be done remotely. A rootkit, which is a type of malware, also does not require the attacker to be near the target machine as it can be installed remotely through other compromised systems or security vulnerabilities.