Data integrity in a relational database can be ensured using SQL constraints such as PRIMARY KEY (to enforce uniqueness), FOREIGN KEY (to maintain referential integrity), CHECK (to validate data), and UNIQUE (to enforce uniqueness).

The correct option is "Hypervisor." A hypervisor, also known as a virtual machine monitor (VMM), allows multiple virtual machines (VMs) to run on a single physical machine by abstracting and managing the underlying hardware resources. It provides isolation, resource allocation, and control over the VMs, enabling different operating systems to coexist on the same hardware.

Abstraction in OOP refers to the concept of hiding complex implementation details and showing only essential features of an object. Encapsulation, on the other hand, involves bundling the data (attributes) and methods (functions) that operate on the data into a single unit, i.e., a class. This helps in achieving data hiding and access control.

Option 1 is correct. In a social media platform, it's efficient to have separate tables for users, profiles, and relationships. This allows for easier management and scalability. Foreign keys ensure data integrity and help in querying related information efficiently. Using a single table for users can lead to data redundancy and maintenance issues. A hierarchical structure may become complex and harder to manage as the platform scales. Denormalization, while useful in certain cases, may not be ideal for handling user profiles and relationships in a social media context.

When resolving conflicts in Git, the first step is to identify the conflicting files. git status helps in listing the conflicting files. Once identified, use git diff to view the differences and manually resolve the conflicts in the file. After resolving the conflicts, stage the changes with git add and then commit the resolved changes. Alternatively, you can also use tools like git mergetool to help with resolving conflicts more efficiently.

File system fragmentation occurs when files are broken into pieces scattered across the disk, leading to increased read/write times as the system needs to access multiple fragments. This impacts performance as it introduces delays in retrieving and storing data.

The correct answer is 'classes.' CSS classes allow you to apply the same styling to multiple HTML elements by assigning the class name to those elements.

Achieving Transitive Dependency Elimination

To improve security in Node.js applications, developers should use Helmet, a middleware package that helps in securing Express apps by setting various HTTP headers to prevent common vulnerabilities like XSS attacks.

A Priority Queue is the most efficient data structure for managing tasks with varying levels of urgency in a concurrent execution system. It ensures that tasks are executed based on their priority levels, allowing higher priority tasks to be processed before lower priority ones. This is crucial for maintaining system responsiveness and meeting urgent task requirements promptly. Binary Search Trees, Hash Tables, and Doubly Linked Lists are not specifically designed for priority-based task management and may not offer the same level of efficiency and responsiveness as a Priority Queue.