system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
from flask import Blueprint, render_template, url_for, flash, request, redirect
from flask_login import login_user, current_user, logout_user, login_required
from app import db, bcrypt
from app.users.forms import RegistrationForm, LoginForm, UpdateAccountForm, RequestResetForm, ResetPasswordForm
from app.users.utils import save_picture, send_reset_email
from app.models import User, Post


users=Blueprint('users', __name__)

@users.route('/register', methods=['POST','GET'])
def register():
    if current_user.is_authenticated:
        return redirect(url_for('main.home'))
    form=RegistrationForm()
    if form.validate_on_submit():
        hashed_password=bcrypt.generate_password_hash(form.password.data).decode('utf-8')
        user= User(username=form.username.data, email=form.email.data, password=hashed_password)
        try:
            db.session.add(user)
            db.session.commit()
            flash(f'Account Created for {form.username.data}!, you can now login :)', category='success')
            return redirect(url_for('users.login'))
        except:
            flash(f'The user is already registered!! Try to login!!', category='danger')    
        

    return render_template('register.html', title='Register', form=form)

@users.route('/login', methods=['POST','GET'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('main.home'))
    form=LoginForm()
    if form.validate_on_submit():
        user=User.query.filter_by(email=form.email.data).first()
        if user and bcrypt.check_password_hash(user.password, form.password.data):
            login_user(user, remember=form.remember.data)
            next_page=request.args.get('next')
            flash(f'Hey {user.username}! Good to see you back ;)', category='success')
            if next_page:
                return redirect(next_page)
            else:
                return redirect(url_for('main.home'))    
        else:
            flash(f'Login Unsuccessful. Please check the email and/or Password', 'danger')  
              
    return render_template('login.html', title='Login', form=form)


@users.route('/logout')
def logout():
    logout_user()
    return redirect(url_for('main.home'))



@users.route('/account', methods=['POST','GET'])
@login_required
def account():
    form=UpdateAccountForm()
    if form.validate_on_submit():
        if form.picture.data:
            picture_file=save_picture(form.picture.data)
            current_user.image_file=picture_file

        current_user.username=form.username.data
        current_user.email=form.email.data
        db.session.commit()
        flash(f'Account Details Updated!!', category='success')
    elif request.method=='GET':
        form.username.data=current_user.username
        form.email.data=current_user.email    
    image_file=url_for('static', filename='profile_pics/'+current_user.image_file)
    return render_template('account.html',title='Account', image_file=image_file, form=form)


@users.route('/user/<string:username>')
def user_posts(username):
    page=request.args.get('page', default=1, type=int)
    user=User.query.filter_by(username=username).first_or_404()
    posts=Post.query.filter_by(author=user).order_by(Post.date_posted.desc()).paginate(page=page, per_page=3)
    return render_template('user_posts.html', posts=posts,user=user)




@users.route('/reset_password',methods=['GET', 'POST'])
def reset_request():
    if current_user.is_authenticated:
        return redirect(url_for('main.home'))
    form=RequestResetForm()
    if form.validate_on_submit():
        user=User.query.filter_by(email=form.email.data).first()
        send_reset_email(user)
        flash(f'Check Your Registered Email for further instructions', 'info')
        return redirect(url_for('users.login'))
    return render_template('reset_request.html',title='Reset Password', form=form)



@users.route('/reset_password/<token>',methods=['GET', 'POST'])
def reset_token(token):
    if current_user.is_authenticated:
        return redirect(url_for('main.home'))
    user=User.verify_reset_token(token)
    if user is None:
        flash(f'That is an invalid or expired token', 'warning')
        return redirect(url_for('login.reset_request'))
    form=ResetPasswordForm()
    if form.validate_on_submit():
        hashed_password=bcrypt.generate_password_hash(form.password.data).decode('utf-8')
        user.password=hashed_password
        db.session.commit()
        flash(f'Password Updated! You can now login :)', category='success')
        return redirect(url_for('users.login'))
    return render_template('reset_token.html',title='Reset Password',form=form)      
```

Which of the following functions or classes contains a `CWE-601: URL Redirection to Untrusted Site ('Open Redirect')` vulnerability?

  A) logout
  B) account
  C) reset_request
  D) login
Answer: D