Which scenario exemplifies shoulder surfing?

Shoulder surfing refers to the act of discreetly observing someone's private information, typically through direct observation. In this case, the scenario where someone steals your password after watching you type it perfectly illustrates this concept. The act of watching you enter your password from a close distance constitutes shoulder surfing because it involves the unauthorized observation of sensitive data being inputted.

The other options, although they depict security concerns, do not specifically relate to shoulder surfing. Following someone into a restricted area involves physical security breaches, while an email that appears to be from a trusted source refers more to phishing and social engineering tactics. A video recording of you entering sensitive information pertains to surveillance and unauthorized recording rather than the act of closely watching someone in person. Thus, option A is the most accurate representation of shoulder surfing.