title: how to delete lines connected with "+" signs with sed
body: <p>In this example, "+" sign means it connects the previous line and the current line. So I like to delete a specific group of lines that are connected by "+". 
  For example, I'd like to remove from 1st line to 4th line(.groupA ~ + G H I). Please help me on how to do it with sed.</p>
  
  <p><img src="https://i.stack.imgur.com/7WekU.png" alt=""></p>