What is the function of backtick (`) characters in PHP?

You want to run the following PHP 4 code with PHP 5. In the following example, which access
modifier in PHP 5 is equivalent to “var”?
<code>
class Test {
var $tester;
}
</code>

Which of the listed changes would you make to the following PHP 4 code in order to make it most
compliant with PHP 5? (Choose 2)
<code>
<?php
class Car {
var $model;
function Car($model) {
$this->model = $model;
} function toString() {
return “I drive a $this->model.”;
}}
$c = new Car(‘Dodge’);
echo $c->toString();
?>
</code>