Which of the following best describes a social engagement ad$?$

a$.$

Contains ad creative $($image and text$),$ along with an option to encourage the viewer to engage with the brand.

b$.$

Includes ad creative, an engagement device, and personalized referral content from people in the viewer's network.

c$.$

Is shared on a person's activity stream following a brand interaction $($such as liking the brand$).$

d$.$

Motivates the receiver to get involved with the message and help spread it to others.

e$.$

Occurs when an opinion leader publishes brand$-$relevant content, such as a blog post in social media.