In order to encourage participation in a walkathon, the organization arranging the event offers free items, such as a T-shirt or a water bottle, to all the participants. Which of the following principles of influence is being used?
A. liking
B. authority
C. scarcity
D. reciprocation
E. social proof

The correct answer is letter "E": social proof.

Explanation:

In marketing, Social Proof is nothing more than a demonstration of the use of a product or service by a group of people so others can be encouraged to purchase it. Social proof has proven effectiveness as a way to influence others and every time on the internet and social media it tends to facilitate businesses more leverage more over at the moment of introducing goods in the market so more people are willing to buy those products or services.

two years ago, when picking flowers in the mountains back of yosemite valley, i found a book. it was blotted and storm-beaten; all of its outer pages were mealy and crumbly. the paper seemed to dissolve like the snow beneath which it had been buried, however; many of the inner pages were well preserved. and although all were more or less stained and torn, whole chapters were easily readable. this is the condition of the great open book of yosemite glaciers today; its granite pages have been torn and blurred by the same storms that wasted the castaway book.

two years ago, when picking flowers in the mountains back of yosemite valley; i found a book. it was blotted and storm-beaten, all of its outer pages were mealy and crumbly. the paper seemed to dissolve like the snow beneath which it had been buried, however, many of the inner pages were well preserved. and although all were more or less stained and torn; whole chapters were easily readable. this is the condition of the great open book of yosemite glaciers today, its granite pages have been torn and blurred by the same storms that wasted the castaway book.