php - How to get the Facebook apps permission from Facebook Inc. to public the app

I have developed Facebook Canvas application to take survey and also to collect the user's timeline data those who took survey. I have used "user_posts" permission to collect user's timeline public posts. These public posts is require to do my PhD research.

I have done all the prerequisite steps before submitting my facebook apps approval from Facebook but Facebook unapproved my application by saying that

"user_posts : Provides access to the posts on a person's Timeline, including their own posts and posts from others. on Canvas - This permission request doesn't meet our criteria for approval. Please only request permissions that you need to create a high quality, personalized in-app experience for people."

Facebook criteria for approval for user_posts is given here https://developers.facebook.com/docs/facebook-login/permissions#reference

Where they have mentioned that :

- user_posts : Provides access to the posts on a person's Timeline. Includes their own posts, posts they are tagged in, and posts other people make on their Timeline.

- Review: If your app requests this permission Facebook will have to review how your app uses it.

- Common Usage:

• Provide creative content from Timeline posts. [approved]

• Provide value to the user by visibly analyzing the content of the posts on their Timeline.[approved]

• Non-visible use of this data such as sentiment analysis or guarding against spam bots. [not-approved]

I have tried it several time, but not able to get the apps permission for my facebook canvas app. How can I know that if I develop an application that FB will not deny it even if it meets conditions of usage? How to get the permission for "user_posts"? Do some one have the experience in developing FB apps? It would be very much helpful to get the reply from facebook apps developer who have done it before.

Thanks and regards