Mobile Device Management (MDM) allows an organization to enforce security policies, such as denying network access to jailbroken/rooted devices.
From the All-in-One Exam Guide by Travis Everett and Andrew Hutz:
"MDM software allows administrators to monitor, manage, and secure mobile devices connected to enterprise networks. One key feature is the detection and denial of access for rooted or jailbroken devices".
Quentin Docter also confirms:
"An MDM solution can check if a device has been rooted and prevent it from accessing the network, ensuring compliance with corporate security standards".

The symptoms point to malicious or rogue content: frequent "security warning" pop-ups that push "tools" is a classic sign of scam/rogue apps, and the new fast battery drain suggests an unwanted process running in the background. The CompTIA objectives explicitly list mobile security symptoms such as "high number of ads,"
"fake security warnings," and "unexpected application behavior," which aligns with this scenario. On the browser side, Quentin Docter notes that if you continually receive pop-ups or overlays, "you may be infected with malware," and recommends scanning with antivirus/antimalware software. He also explains that clearing browsing data/cache is sometimes necessary to resolve browser-related problems and details how to clear cache/browsing data.
Because the user tapped the pop-up and then battery life worsened, the best practical fix is to remove the likely malicious application(s) (uninstall unknown apps) and clear browser cache to eliminate stored site data
/scripts fueling the pop-ups. A factory reset is a stronger last resort, but least disruptive remediation is A.

A low-level format (also referred to as a zero-fill or full format) writes over every sector on a storage device, effectively destroying the existing data and making recovery nearly impossible. Unlike degaussing, which renders the drive unusable, a low-level format maintains the integrity of the device, allowing it to be repurposed or reused.
A). Deleting partitions does not fully erase data; it only removes references in the partition table.
B). EFS (Encrypting File System) encrypts files but does not securely wipe them.
D). Degaussing destroys the magnetic structure of a drive, making it inoperable and not reusable.
Reference:
CompTIA A+ 220-1102 Objective 4.3: Given a scenario, implement basic change management best practices.
Study Guide Section: Drive sanitation methods - low-level format vs. degaussing vs. deletion

The correct answer is D. Roaming profiles, because roaming profiles allow users to log in to any domain- joined workstation and automatically access their personal settings, documents, and configuration without storing data locally on each machine. This is ideal for environments with hot-desking or shared workstations.
According to the Quentin Docter - CompTIA A+ Complete Study Guide, roaming profiles store user data centrally on a server rather than on individual computers. When a user logs in, their profile is loaded; when they log out, changes are saved back to the server. This minimizes data duplication and reduces the risk of data being left behind on shared systems.
The Travis Everett & Andrew Hutz - All-in-One Exam Guide emphasizes that roaming profiles improve security by preventing sensitive user data from being permanently stored on multiple endpoints. This also simplifies backup and recovery, since user data resides in a centralized location.
The Mike Meyers / Mark Soper Lab Manual clarifies that portable drives introduce data loss risks, cloud email only addresses messaging data, and certificate storage does not manage user profiles or documents.
Because the goal is to maintain data security while allowing mobility and minimizing data transfer, roaming profiles are the most appropriate solution, making D the correct answer.

MDM hardening often includes enforcing stronger authentication on mobile devices. The phrase "unique to each user" points to something inherent to the individual-biometrics-rather than something the user knows (password/pattern) or something they have (PIV/smart card). Quentin Docter explains: "Biometric devices use physical characteristics to identify the user. This type of authentication is considered something that you are," and lists common implementations including "fingerprint... scanners." This exactly matches a fingerprint, which is unique per person and commonly enforced via device policies in MDM environments.
Docter also notes mobile devices increasingly implement biometrics for access control, specifically citing
"fingerprint access control" adopted by manufacturers. A drawn pattern and a password are knowledge factors and can be shared/observed, while a PIV card is a possession factor (something you have) and can be lost or loaned. Because the question specifies a hardening technique "unique to each user," the best match is the biometric factor: fingerprint (B).