In PHP, to use inheritance in your script, you would use the extends keyword followed by the name of the parent class. The correct option is "By using the extends keyword." By extending a class, you create a subclass that inherits properties and methods from the parent class. For further details, refer to the PHP documentation on class inheritance: http://php.net/manual/en/language.oop5.inheritance.php

In PHP, the foreach loop allows you to access both the keys and values of an array. During each iteration, you can use the "key" variable to access the key/index of the current element, and the "value" variable to access the value of the element. This allows you to work with both the keys and values simultaneously. The foreach loop provides a convenient way to iterate over arrays and perform operations on each element. Learn more: https://www.php.net/manual/en/control-structures.foreach.php

The filter_list() function is used to get the list of all supported filters in PHP. It returns an array containing the names of all available filters. For more details, visit: http://php.net/manual/en/function.filter-list.php

Potential issues when handling forms in PHP can include security vulnerabilities due to inadequate input validation and sanitization. Improper handling of user-submitted data can lead to security risks such as cross-site scripting (XSS) or SQL injection attacks. Performance issues may arise when processing large amounts of form data, especially if inefficient code or database operations are involved. In PHP, accessing form data using superglobal arrays like $_POST or $_GET is straightforward and does not pose significant issues. Styling form elements is primarily handled through HTML and CSS, so PHP's form handling itself does not have limitations in this aspect. Learn more: https://www.php.net/manual/en/tutorial.forms.php

PHP supports different ways to add comments. Single-line comments can be denoted with double slashes (//) or a hash symbol (#) at the beginning of a line. Multi-line comments can be enclosed between /* and */. All of the provided options are valid ways to add comments to PHP code.

To access specific data from the $_REQUEST superglobal in PHP, you can use the $_REQUEST['fieldname'] syntax. Here, 'fieldname' refers to the name of the input field or key from which you want to retrieve the data. For example, if you have an input field with the name 'username', you can access its value using $_REQUEST['username']. By using the appropriate field name as the key within the $_REQUEST array, you can retrieve the desired data. Learn more: https://www.php.net/manual/en/reserved.variables.request.php

Abstract classes in PHP can have method implementations, allowing you to define common behavior for its subclasses. Interfaces, on the other hand, only define method signatures that must be implemented by classes. Abstract classes are used when you want to create a base class that provides common functionality, while interfaces are used to define a contract that multiple classes can adhere to. Knowing when to use each depends on the specific requirements of your application. For more information, you can refer to the PHP documentation: http://php.net/manual/en/language.oop5.abstract.php, http://php.net/manual/en/language.oop5.interfaces.php

Unlike variables, constants in PHP are automatically declared. Once defined using the define() function, constants are available throughout the script without the need for additional declaration statements. They are immediately ready for use. On the other hand, variables need to be explicitly declared using the $ sign before they can be used. This automatic declaration of constants makes them easily accessible and convenient to use in PHP scripts. Learn more: https://www.php.net/manual/en/language.constants.php

If the mysqli_query function returns false, it means the query execution failed. To get the error message, you can use the mysqli_error function. It takes the connection object ($conn) as a parameter and returns the error message associated with the most recently executed query. You can display the error message using echo, for example: "Error creating table: " . mysqli_error($conn). This helps in troubleshooting and identifying any issues that occurred during the query execution. Ensure you have a successful connection and have executed a query before checking for errors.

When using FTP functions in PHP, you might encounter potential issues such as connection failures, authentication problems, or file transfer errors. Connection failures can occur due to network issues, server unavailability, or incorrect FTP server settings. Authentication issues may arise if the provided credentials are incorrect or if the FTP server has strict authentication requirements. File transfer errors can happen if the remote file does not exist, the local file is not readable, or if there are restrictions on file permissions. It's important to handle these issues by validating input, checking return values, and implementing error handling mechanisms to ensure successful FTP operations in PHP.