How Do Most Current Social Media Platforms Generate Revenue

How do most current social media platforms generate revenue?

A) A majority of social media platforms employ a subscription-based business model where users must purchase a monthly subscription to use the service
B) Social media sites run purely on donations from sizable third party organizations to sustain their operations
C) To use social media platforms, users must purchase a one-time entry fee to use the service, but then may upgrade their service at a later time
D) Many accrue revenue from collecting personal information from their users' online activities then selling that information to marketing and advertising companies