To drive awareness about serious problems in the developing world, the nonprofit organization Water is Life launched a "Hashtag Killer" campaign. This campaign posted videos on YouTube of Haitians reading tweets to excite individuals to donate to their cause. This was an example of

a. a site offering analytical information about website usage

b. an experimental, media-sharing site

c. a video-sharing site intended for business

d. a website where users can work together to create documents

e. the use of the microblog site Twitter