HTML表单不能从PHP页面打印？

I have an html page that collects data using a form with the multiple attribute, but when I try to echo out the data on the PHP page, it only echos out the last item selected.

  <select name="cars" multiple>
   <option value="car1"> BMW </option>
   <option value="car2"> TOYOTA </option>
   <option value="car3"> HONDA </option>

If I select BMW and TOYOTA, and try to echo $_POST['cars']; all it echos out is TOYOTA and not BMW. How do I get it to echo out everything that is selected?

Make select name as array type. like this and print_r($_POST['cars']);

<select name="cars[]" multiple>
   <option value="car1"> BMW </option>
   <option value="car2"> TOYOTA </option>
   <option value="car3"> HONDA </option>