Getting a random number of 'pipe images' out

Cocos Creator
#1

Hi, I’m While studying ‘tutorial-duang-sheep-master’, I got a question.
Only one pipe keeps coming out. but I want to alternate images.
How do I put another ‘prepab’ together so that the two come in turn?

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cc.Class({
extends: cc.Component,
properties: {
pipePrefab: cc.Prefab,
pipeLayer: cc.Node,
initPipeX: 0,
spawnInterval: 0
},
onLoad () {
D.pipeManager = this;
},
startSpawn () {
this.spawnPipe();
this.schedule(this.spawnPipe, this.spawnInterval);
},

spawnPipe () {
    let pipeGroup = null;
    if (cc.pool.hasObject(PipeGroup)) {
        pipeGroup = cc.pool.getFromPool(PipeGroup);
    } else {
        pipeGroup = cc.instantiate(this.pipePrefab).getComponent(PipeGroup);
    }
    this.pipeLayer.addChild(pipeGroup.node);
    pipeGroup.node.active = true;
    pipeGroup.node.x = this.initPipeX;
},
despawnPipe (pipe) {
    pipe.node.removeFromParent();
    pipe.node.active = false;
    cc.pool.putInPool(pipe);
},
reset () {
    this.unschedule(this.spawnPipe);
}

});