To use image functions in PHP, you need to have the GD (Graphics Draw) library enabled. The GD library is a popular image manipulation library that provides a set of functions to create, modify, and output images. It supports various image formats and allows you to perform operations like resizing, cropping, adding text, and applying filters to images. The GD library needs to be installed and enabled in your PHP configuration for the image functions to work.

In PHP, you can start a session by using the session_start() function. This function initializes a new session or resumes an existing session. It needs to be called at the beginning of your PHP script before any session variables are accessed. Refer to: http://php.net/manual/en/function.session-start.php

PHP scripts are enclosed within tags. These tags can be inserted anywhere in the document. The PHP interpreter only reads the code inside these tags. Learn more: https://www.php.net/manual/en/language.basic-syntax.phptags.php

False. In PHP, the keys in an indexed array are not always strings. Indexed arrays use numeric keys that are automatically assigned, starting from 0. These keys are integers and not strings. The numeric keys allow for easy access and manipulation of array elements based on their position within the array. Learn more: https://www.php.net/manual/en/language.types.array.php#language.types.array.syntax

The filter_var() function in PHP is used to filter and validate data. It provides a wide range of filters to sanitize and validate various types of data, such as URLs, email addresses, numbers, and more. By applying appropriate filters, the filter_var() function helps ensure data integrity and security. Refer to: http://php.net/manual/en/function.filter-var.php

In PHP, variable names must start with a dollar sign ($), followed by the name of the variable. The variable name is case-sensitive. Variable names follow certain rules: they must begin with a letter or the underscore character; they can't begin with a number; they can contain alpha-numeric characters and underscores. Learn more: https://www.php.net/manual/en/language.variables.basics.php

In PHP, the float keyword is used to declare a floating-point number. Floats, also known as floating-point numbers or doubles, are used to represent real numbers with a decimal point. They can hold positive and negative values with varying degrees of precision. Learn more: https://www.php.net/manual/en/language.types.float.php

In PHP, a class implements an interface using the implements keyword followed by the name of the interface or a comma-separated list of interface names. For example: class ClassName implements InterfaceName { } By implementing an interface, a class agrees to fulfill the contract defined by the interface. The class must provide an implementation for all the methods defined in the interface. A class can implement multiple interfaces by listing them after the implements keyword. This allows the class to define behavior and functionality according to multiple contracts. To know more about interface implementation, visit: http://php.net/manual/en/language.oop5.interfaces.php

The correct option is 4. Array sorting functions in PHP have various common uses. They are used to display data in a specific order, such as sorting records in ascending or descending order based on a specific column. Sorting functions can also be used in searching algorithms to locate specific elements in an array more efficiently. Additionally, array sorting functions are used to reorder elements for better organization, such as rearranging an array of strings in alphabetical order. The versatility of array sorting functions allows for effective data organization and retrieval in a wide range of PHP applications. Learn more: https://www.php.net/manual/en/array.sorting.php

Common practices in PHP when using Object-Oriented Programming (OOP) include properly documenting classes and their members to provide clear usage instructions and guidelines. Following SOLID principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) helps in designing maintainable and flexible code. Implementing design patterns, such as Factory, Singleton, and Observer, can enhance code organization and provide reusable solutions to common problems. The correct option is "Properly documenting classes and their members, Following SOLID principles, Implementing design patterns." For further details, refer to the PHP documentation on object-oriented programming: http://php.net/manual/en/language.oop5.php