actionscript 3 - How can i hitTesObject a movieclip inside a movieclip AS3? -

i want zombie collect brains(g1b1,g1b2,g1b3,g1b4). these brains inside movieclip 'platform1' because need have scrolling background effect. zombie character can walk can't collect brains.

import flash.display.movieclip; import flash.events.keyboardevent; import flash.events.event; import flash.ui.keyboard; import flash.display.sprite;  public class z extends movieclip {      private var score:int=0;     private var zombiespeed:int=7; //speed zombie     private var gravity:int=1;     private var jumpspeed:int=0;//current speed jump     private var jumpspeedlimit:int=15; //how quick jump      private var jump, left, right, down, mainjump:boolean=false; //zombie not jumping      public function z() {      }      public function game1() {         stop();         stage.addeventlistener(keyboardevent.key_down, keypressed);         stage.addeventlistener(keyboardevent.key_up, keyreleased);         zombie.addeventlistener(event.enter_frame, movecharacter1);         gameplay1();     }      private function keypressed(e:keyboardevent) {         if (e.keycode==keyboard.left) {             left=true;             zombie.gotoandplay("left");         }         if (e.keycode==keyboard.right) {             right=true;             zombie.gotoandplay("right");         }         if (e.keycode==keyboard.space || keyboard.up) {             jump=true;         }         if (e.keycode==keyboard.down) {             down=true;         }     }      private function keyreleased(e:keyboardevent) {         if (e.keycode==keyboard.left || keyboard.d) {             left=false;             zombiespeed-=5;             zombie.gotoandstop("idleleft");         }         if (e.keycode==keyboard.right || keyboard.a) {             right=false;             zombiespeed+=5;             zombie.gotoandstop("idleright");         }         if (e.keycode==keyboard.space || keyboard.up || keyboard.w) {             jump=false;         }         if (e.keycode==keyboard.down || keyboard.s) {             down=false;         }     }      private function movecharacter1(e:event) {         if (left) {             if (platform1.x<1000 && zombie.x==870) {                 platform1.x+=5;             }             else {                 if (zombie.x>120) {                     zombie.x-=zombiespeed;                     trace(platform1.x);                 }             }         }         if (right) {             if (platform1.x>0 && zombie.x==870) {                 platform1.x-=5;             }             else {                 if (zombie.x<880) {                     zombie.x+=zombiespeed;                     trace(platform1.x)                 }             }         }         if (jump) {             gojump();     }      function gojump() {         if(jumpspeed > 0 && jumpspeed <= jumpspeedlimit){             jumpspeed *= 1 + jumpspeedlimit/50;         }         zombie.y += jumpspeed;               (var i=0;i<5;i++) {             if(platform1.hittestpoint(zombie.x,zombie.y,true)) {                 zombie.y--;                 jumpspeed=0;                 mainjump=false;             }         }     }      **private function gameplay1() {         if(zombie.hittestobject(platform1.g1b1)){             platform1.g1b1.visible = false;             score+=10;         }         if(zombie.hittestobject(platform1.g1b2)){             platform1.g1b2.visible = false;             score+=10;         }         if(zombie.hittestobject(platform1.g1b3)){             platform1.g1b3.visible = false;             score+=10;         }         if(zombie.hittestobject(platform1.g1b4)){             platform1.g1b4.visible = false;             score+=10;         }           }**  }