How to hitTest with attachMovie

programming flash
1

Please help me, my script below is not working perfectly, Need any correction to my script below, What i want in this animation is Everytime ObjC3 hit ObjCat, then ObjC3 change to other shape, and if ObjC3 _y position less than 0 than this shape change to previous shape :

 
    wRx=128;
    hRx=429;
    TopRx=0
    BtmRx=TopRx+hRx;
    LRx=0;
    RRx=LRx+wRx;
//Object Propylene (C3)
for(i=5;i<=15;i++){
ObjC3=Rx.forC3inRx.attachMovie("id_c3","id_c3"+i,i);
    ObjC3._x=random(wRx);
    ObjC3._y=random(hRx);
    ObjC3._alpha=0;
    ObjC3.xSpeed=0;
    ObjC3.ySpeed=0;
    ObjC3.LSpeed=2;
    ObjC3.HSpeed=10;
    ObjC3.Speed=5;
    ObjC3.shape=0
ObjC3.onEnterFrame=function(){    
    //Movement Down>>Up
    this._y -=random(this.Speed);
    if(this._y<=TopRx){this._y=BtmRx}
    //Alpha
    this._alpha +=random(2);}
}
//Object Catalyst
for(c=25;c<=35;c++){
    ObjCat=Rx.forCatinRx.attachMovie("id_cat","id_cat"+c,c);
    ObjCat._x=random(wRx);//xPos;
    ObjCat._y=random(hRx);//yPos;
    ObjCat._alpha=0;
    ObjCat.xSpeed=0;
    ObjCat.ySpeed=0;
    ObjCat.LSpeed=2;
    ObjCat.HSpeed=10;
    ObjCat.Speed=4;    
    //
ObjCat.onEnterFrame=function(){
    //Movement Up>>Down
    this._y +=random(this.Speed);
    if(this._y>=BtmRx){this._y=TopRx}
    this._alpha +=random(2);}
}
//Test Hit
    if(ObjC3.hitTest(ObjCat)){
        ObjC3.gotoAndStop(2);
        ObjC3.shape=1;}
    if(ObjC3.shape==1 && ObjC3._y<=0){
        ObjC3.gotoAndStop(1);
        ObjC3.shape=0;}