You are a developer at a social media company. The company runs their social media website on-premises and uses MySQL as a backend to store user profiles and user posts. Your company plans to migrate to Google Cloud, and your learn will migrate user profile information to Firestore. You are tasked with designing the Firestore collections. What should you do?

A. Create one root collection for user profiles, and create one root collection for user posts. B. Create one root collection for user profiles, and create one subcollection for each user's posts. C. Create one root collection for user profiles, and store each user's post as a nested list in the user profile document. D. Create one root collection for user posts, and create one subcollection for each user's profile.