railsチュートリアル第11章の途中でsign upをしたらArgumentError in Users#createとエラーが出てしまい解決できずに困っています。

前提・実現したいこと

railsチュートリアルの第11章の途中でsign upをしたら
ArgumentError in Users#createというエラーが出てしまい、
色々試したのですがどうしても解決できず困っています。

メールのアカウント有効化系の実装をしていてエラーが出たと思われます。
（曖昧ですみません。）

発生している問題・エラーメッセージ

エラー名→「ArgumentError in Users#create」


Showing /home/ec2-user/environment/sample_app/app/views/user_mailer/account_activation.html.erb where line #9 raised:

Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true

該当のソースコード

・ファイル名→「account_activation.html.erb」

・以下コード↓
<h1>Sample App</h1>

<p>Hi <%= @user.name %>,</p>

<p>
Welcome to the Sample App! Click on the link below to activate your account:
</p>

<%= link_to "Activate", edit_account_activation_url(@user.activation_token,email: @user.email) %>

・ファイル名→「user_mailer.rb」

・以下コード↓
class UserMailer < ApplicationMailer

  def account_activation(user)
    @user = user
    mail to: user.email, subject:"Account activation"
  end

  def password_reset
    @greeting = "Hi"

    mail to: "to@example.org"
  end
end

・ファイル名→「users_controller.rb」

・以下コード↓
class UsersController < ApplicationController
  before_action :logged_in_user,only:[:index,:edit,:update,:destroy]
  before_action :correct_user,only:[:edit,:update]
  before_action :admin_user,only: :destroy

  def index
    @users = User.paginate(page:params[:page])
  end

  def show
    @user = User.find(params[:id])
  end

  def new
    @user = User.new
  end

  def create
    @user = User.new(user_params)
    if @user.save
      UserMailer.account_activation(@user).deliver_now
      flash[:info] = "Please check your email to activate your account."
      redirect_to root_url
    else
      render 'new'
    end
  end
  
  def edit
  end
  
  def update
    if @user.update_attributes(user_params)
      flash[:success] = "Profile updated"
      redirect_to @user
    else
      render'edit'
    end
  end
  
  def destroy
    User.find(params[:id]).destroy
    flash[:success]="User deleted"
    redirect_to users_url
  end

  private

    def user_params
      params.require(:user).permit(:name, :email, :password,
                                   :password_confirmation)
    end
    
    def logged_in_user
      unless logged_in?
      store_location
        flash[:danger] ="Please log in."
        redirect_to login_url
      end
    end
    
    def correct_user
      @user=User.find(params[:id])
      redirect_to(root_url)unless current_user?(@user)
    end
    
    def admin_user
      redirect_to(root_url) unless current_user.admin?
    end
end

・ファイル名→「development.rb」

・以下コード↓
Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.

  # In the development environment your application's code is reloaded on
  # every request. This slows down response time but is perfect for development
  # since you don't have to restart the web server when you make code changes.
  config.cache_classes = false

  # Do not eager load code on boot.
  config.eager_load = false

  # Show full error reports.
  config.consider_all_requests_local = true

  # Enable/disable caching. By default caching is disabled.
  if Rails.root.join('tmp/caching-dev.txt').exist?
    config.action_controller.perform_caching = true

    config.cache_store = :memory_store
    config.public_file_server.headers = {
      'Cache-Control' => "public, max-age=#{2.days.seconds.to_i}"
    }
  else
    config.action_controller.perform_caching = false

    config.cache_store = :null_store
  end

  # Don't care if the mailer can't send.
  
  config.action_mailer.rails_delivery_errors = true
  config.action_mailer.delivery_method =:test
  host ='a74a1e0d17164030933c4775e8454142.vfs.cloud9.ap-southeast-1.amazonaws.com'
  config.action_mailer.default_url options = {host:host,protocol:'https'}

  config.action_mailer.perform_caching = false

  # Print deprecation notices to the Rails logger.
  config.active_support.deprecation = :log

  # Raise an error on page load if there are pending migrations.
  config.active_record.migration_error = :page_load

  # Debug mode disables concatenation and preprocessing of assets.
  # This option may cause significant delays in view rendering with a large
  # number of complex assets.
  config.assets.debug = true

  # Suppress logger output for asset requests.
  config.assets.quiet = true

  # Raises error for missing translations
  # config.action_view.raise_on_missing_translations = true

  # Use an evented file watcher to asynchronously detect changes in source code,
  # routes, locales, etc. This feature depends on the listen gem.
  config.file_watcher = ActiveSupport::EventedFileUpdateChecker
  
end