Read the paragraph about social media.

social media outlets are often criticized as forums for unimportant postings and uniformed rants. though much of what is posted is conversational drivel, social media outlets also serve as springboards for entrepreneurs. creative people can advertise their designs or products at a low cost to a wider market than entrepreneurs could have imagined in previous generations. the internet is the ultimate free marketplace, allowing motivated individuals to share their wares with the world.

what is the controlling idea?

every entrepreneur should advertise one’s products on the internet.
the internet has countless forums on which people share meaningless posts.
social media has a valid purpose as an inexpensive, creative marketplace.
advertising products on the internet is inexpensive compared to television.