Php-data transfer between the linkage drop-down list and php and htm

The value of dis.htm between php-linkage drop-down lists and php?htm=& lt; div & nbsp; & gt; & lt; span & gt; destination city & lt; span & gt; & nbsp; & lt; select & nbsp; namecontent & gt; & lt; option & nbsp; valu php-value transfer between the linkage drop-down list and php and htm
Dis.htm

Destination CityContinents
   $ Con [name]
    Country
   $ Cou [name]
    Region
   $ Dis [name]
    Province
   $ Pro [name]
    City
   $ Ci [name]
   

Dis. php

//……
$country=getBycontent($content);
$pro=getBycountry($country);
//……

I want the first drop-down list to be selected and the second drop-down list to appear, and search for the list items in the second drop-down list based on the selected options in the first drop-down list. How can I transfer values between these two files?
------ Solution ----------------------
Demo. php

 
Demo