如何在基于UserCreationForm的类中添加选择字段？

from django import forms
from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth.models import User

class CustomUserCreationForm(UserCreationForm):
    CHOICES = (
        ('option1', 'Option 1'),
        ('option2', 'Option 2'),
        ('option3', 'Option 3'),
    )
    custom_field = forms.ChoiceField(choices=CHOICES)

    class Meta:
        model = User
        fields = ('username', 'password1', 'password2', 'custom_field')

from django.shortcuts import render, redirect
from .forms import CustomUserCreationForm

def register(request):
    if request.method == 'POST':
        form = CustomUserCreationForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('home')
    else:
        form = CustomUserCreationForm()
    return render(request, 'register.html', {'form': form})