The sprintf() function in PHP is used to return a formatted string. It allows you to create formatted strings using placeholders and values, similar to printf() in C.

The correct option is 'count().' In dynamic forms, where the number of fields can change, using 'count()' helps ensure data integrity by determining how many fields have been submitted and handling them appropriately. This is important for server-side validation.

To call a user-defined function in PHP, you simply use the function name followed by parentheses. For example, 'myFunction()' would call the function 'myFunction'.

You can restrict the maximum file size for uploads in PHP through a form by setting the upload_max_filesize directive in the php.ini configuration file. This directive limits the size of uploaded files.

The non-scalar data type in PHP is an array. Arrays can hold multiple values and are not considered scalar because they are collections of values, not single values. Scalars include integers, strings, and booleans.

The $_GET superglobal array is used to collect form data sent via the GET method in PHP. It retrieves data from the URL's query string.

The function rsort is used to sort an indexed array in descending order, preserving the key-value associations.

The PHP superglobal $_POST is used to collect form data sent via the POST method, allowing you to access form input data securely.

To retrieve form data sent using the POST method in PHP, you should use the $_POST superglobal. It contains the form data as an associative array, making it easy to access and process user input.

To pass an argument by reference in PHP, you prepend it with the '&' symbol. This allows the function to modify the original variable passed as an argument.