Hello, a stupid question but...

page_A.php is a page with a form.
The user inserts text in four fields, then he clicks a submit button.
The data goes to page_B.php:
this page controls the data submitted, then echoes a message.
If there were problems with the submitted data the message says:
"a problem occurred with your data. Click here to come back to the
form" (page_A.php).
When the user comes back, he finds the fields white.

How can I do to show him what he submitted?

Thanks!