掲示板を作っているが、コンテンツごとにページの変遷先を変更する方法がわからない

Question

ページによって飛び掲示板を変えたいのに、全部同じ掲示板に飛んでいく。
自分の大学の大学生が使うサービスで、講義の感想を書く。講義の感想を投稿するページからその講義に関する感想を投稿する別の掲示板に飛びたい。

やったこと
rails g controller topics index show
rails g model topic title:string body:content

現状
トップページ→→学年→科目の感想を投稿し、表示するページ（ここからさらにこの学年、科目についての別の掲示板に飛びたい）

views

top.html.erb

<div class="gakunen-main">
<h3>学年を選択してください</h3>

<p class="text-center">
<%= link_to "1年生", "/years/1", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "2年生", "/years/2", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "3年生", "/years/3", class: "btn btn-lg btn-primary btn-block" %><%= link_to "4年生", "/years/4, class: "btn btn-lg btn-primary btn-block" %></br></p>
</div>

show.html.erb

<div class="gakunen-main">
<% provide(:title, "クラスの選択") %>
<h3>クラスを選択してください</h3>

<p class="text-center">
　　　　　<%= link_to "#{@a}年1組", "/#{@a}/1", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年2組", "/#{@a}/2", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年3組", "/#{@a}/3", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年4組", "/#{@a}/4", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年5組", "/#{@a}/5", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年6組", "/#{@a}/6", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年7組", "/#{@a}/7", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年8組", "/#{@a}/8", class: "btn btn-lg btn-primary btn-block" %></br><%= link_to "#{@a}年9組", "/#{@a}/9", class: "btn btn-lg btn-primary btn-block" %></br></p>
</div>

index.html.erb

<div class="subject-main">
<% provide(:title, "講義一覧") %>

<h3>講義を選択してください</h3>
<% @subjects.each do |subject| %>

<div class="aaa">
<p class="text-center">
<%= link_to subject.name, "/subjects/#{subject.id}", class: "btn btn-lg btn-primary btn-block" %></br></p>

<% end %>
</div>

show.html.erb

<div class="note-main">

<% provide(:title, @subject.name+"のページ") %>

<h3><div class="name"><%= @subject.name %>の教授の講義について<div></h3>
  <% if logged_in? %>
      <h1>投稿する</h1>
      <%= form_tag("/posts/create") do %>
            <textarea name="content"></textarea>
            <%= hidden_field_tag "subject_id", @subject.id %>
            <input type="submit" value="投稿"　class: "btn btn-primary">
      <% end %>
      <% else %>
    <h3><%= link_to "投稿するにはログインが必要です", login_path %></h3>
    <% end %>


<%= will_paginate @posts %>



    <% @posts.each do |post| %>
      <div class="posts-index-item">
        <strong>『<%= post.content %>』</strong>　by <%= post.user.name  %>



        <% if logged_in? %>
        <% if Like.find_by(user_id: @current_user.id, post_id: post.id) %>
            <<%= link_to("/likes/#{post.id}/destroy", {method: "post"}) do %>
              <span class="fa fa-heart like-btn-unlike"></span>
              <% end %>
          <% else %>
          <%= link_to("/likes/#{post.id}/create", {method: "post"}) do %>
              <span class="fa fa-heart like-btn"></span>
          <% end %>
          <% end %>
          <%=  Like.where(post_id: post.id).count %>
          <% else %>
        いいねの数:  <%= Like.where(post_id: post.id).count %>
          <% end %>
          <p align=right><%= post.created_at.localtime %></p>
      </div>
 <% end %>



<%= will_paginate @posts %>

</div>

routes

Rails.application.routes.draw do



  post "likes/:post_id/create" => "likes#create"
  post "likes/:post_id/destroy" => "likes#destroy"

  get "posts/index" => "posts#index"
  get "posts/new" => "posts#new"
  get "posts/:id" => "posts#show"
  post "posts/create" => "posts#create"

  get 'kumis/show'

  get 'years/show'

  get 'subjects/index'
  get 'subjects/:id' => 'subjects#show'

    get 'kumis/show'



    root   'static_pages#home'
    get    '/help',    to: 'static_pages#help'
    get    '/screen',    to: 'static_pages#screen'
    get    '/configuration',    to: 'static_pages#configuration'
    get    '/about',   to: 'static_pages#about'
    get    '/contact', to: 'static_pages#contact'
    get    '/top', to: 'static_pages#top'
    get    '/signup',  to: 'users#new'
    get    '/login',   to: 'sessions#new'
    post   '/login',   to: 'sessions#create'
    delete '/logout',  to: 'sessions#destroy'

    get  '/years/:year', to: 'years#show'



    resources :users do
        member do
            get :following, :followers
        end
    end
    resources :account_activations, only: [:edit]
    resources :password_resets,     only: [:new, :create, :edit, :update]
    resources :microposts,          only: [:create, :destroy]
    resources :relationships,       only: [:create, :destroy]


    get '/:year/:kumi', to: 'subjects#index'

  end

subjects_controller.rb

class SubjectsController < ApplicationController
    def index
        @a = params[:year]
        @b = params[:kumi]
        @subjects = Subject.where(year: @a,kumi: @b)
        render 'index'
        end


    def show
        @subject = Subject.find_by(id: params[:id])
        @posts = Post.where(subject_id: @subject.id).paginate(:page => params[:page], :per_page => 10).order(created_at: :desc)
        @current_user = User.find_by(id: session[:user_id])
    end
end

years_controller.rb
``years_controller.rb
class YearsController < ApplicationController

def show
    @a = params[:year]
    
    render 'show'
end

end

show.html.erbのなかにこの講義についての掲示板へのリンクを貼りたいのですが、何をどうすればいいのでしょう？
私のやり方では全て同じtopic_indexへ飛んでしまいます
よろしおく願いいたします