a.php
function a() {
　echo "morning\n";
}
b.php
function b() {
　echo "evening\n";
}
c.php
function c() {
　a();
　echo "hello\n";
　b();
}
index.php
include("a.php");
include("b.php");
include("c.php");
c();

こうじゃね