Which of the following is not valid PHP code?

What's the output? $integer = 5; $string = strval($integer); var_dump($string);

What's the output? $a = (2 == '2') ? true : false; echo $a;

Which array function checks if the specified key exists in the array

Which are valid float values?

Which function will attempt to return a timestamp, in microseconds?

Which functions compare the substrings of the parameters?

Which functions set options in curl script?

The contents of an image file are stored in memory as $imString, but the original file is not available. Of the following, which uses the least amount of code and is a valid method of retrieving the dimensions of $imString?

Best way to iterate and modify every element of an array using PHP 5?

How to check if a directory exists?