Final answer:
The primary reason for encrypting hard drives on laptops is to prevent data access by thieves in case of physical theft, which is option C. Options A, while valid, is secondary, and options B and D are incorrect as they refer to different aspects of security.
Step-by-step explanation:
The real reason for encrypting hard drives on laptop computers is primarily to prevent unauthorized access to sensitive data in the event the laptop is lost or stolen. While encryption also helps to secure data from other local users on the same machine, its crucial role is to ensure that a thief cannot access the data if they gain physical possession of the laptop. This is important because unlike online threats that require a hacker to bypass network security, a lost or stolen laptop presents a direct opportunity for thieves to access data.
Option A is a valid reason but not the primary one since multiple user account control can also manage data visibility between users on the same machine. Option B is inaccurate because hard drive encryption does not protect from online threats as this would be the role of network security measures. Option C is the most accurate as it directly addresses the issue of physical theft of a laptop. Lastly, Option D is incorrect because encryption of hard drives does not secure data transmissions, which are protected by separate encryption protocols like SSL/TLS during transit over a network.