Integrate multiple feedbacks if I select multiple answers.

You could track what someone selects using T/F variables. Then show the appropriate feedback based on values of the variables.

• It might help to review the demo in this post. It's not doing exactly what you want, but it might provide some guidance. TIP: Track Responses to Custom Questions or Surveys | Articulate - Community 

FYI: By itself, Storyline can't compile one long feedback that only includes the text related to the selected items. However, there are various ways to present the appropriate pieces of individual feedback. 

I suggest putting each piece of feedback on its own layer or even its own slide. Then use triggers with conditions to control where the continue/next button takes them. 

• Here's a post with guidance about how to do that: TIP: Let the user choose their path | Articulate - Community 

Michelle's suggestions about unlocking buttons would also work. Or give all the buttons the Initial state of Hidden, and then change the appropriate buttons to Normal based on the variables. However, you won't be able to rearrange the buttons.

It’s worth the effort to learn about variables and trigger conditions, because they provide the real power in Storyline. Here’s more information:

• This post provides an overview of variables. It also links to numerous resources. The Value of Variables | Articulate - Community 
• The User Guide articles about triggers include some about conditions. Storyline 360: Working with Triggers | Articulate - Community