How can the "ungreedy" modifier in preg_replace be utilized to address issues with multiple occurrences of a pattern in a string?

When using preg_replace with a regular expression pattern that matches multiple occurrences in a string, the default behavior is to be "greedy," meaning it will match as much as possible. This can lead to unexpected results when trying to replace specific occurrences. To address this issue, the "ungreedy" modifier can be added to the regular expression pattern to make it match as little as possible.

```php
$string = "Hello, World! Hello, Universe!";
$pattern = '/Hello,.*?/';
$replacement = "Hi, ";
$new_string = preg_replace($pattern, $replacement, $string);
echo $new_string;
```

In this code snippet, the "ungreedy" modifier `?` is added to the regular expression pattern `'/Hello,.*?/'`. This ensures that the pattern matches as little as possible, resulting in the replacement of each individual occurrence of "Hello," with "Hi, " in the string.