问同时使用多个按键输入会在Unity C#中产生意外行为

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using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
    bool LeftControl = false;
    bool LeftShift = false;
    bool LeftAlt = false;
    // Update is called once per frame
    void Update()
    {
        LeftControl = Input.GetKey(KeyCode.LeftControl);
        LeftShift = Input.GetKey(KeyCode.LeftShift);
        LeftAlt = Input.GetKey(KeyCode.LeftAlt);

        if (LeftAlt || LeftShift) fb();
        else fa();
    }

    private void fb()
    {
        print("fb");
        if (LeftControl)
        {
            if (Input.GetKeyDown(KeyCode.Alpha1)) print("leftcontrol");
        }
        else
        {
            if (Input.GetKeyDown(KeyCode.Alpha1)) print("NOleftcontrol");
        }
    }

    private void fa()
    {
        print("fa");
        if (LeftControl)
        {
            if (Input.GetKeyDown(KeyCode.Alpha1)) print("leftcontrol");
        }
        else if(LeftShift)
        {
            if (Input.GetKeyDown(KeyCode.Alpha1)) print("leftshift");
        }
    }
}