Imagine you are writing an argument to convince others that people should become vegetarians. you want people to stop eating meat and start eating nuts and beans for protein. which group of people can you expect to support you without even reading your argument?

a. cattle ranch owners
b. fast food executives
c. state level lawmakers
d. animal rights supporters

D. Animal rights supporters since the other people:
Cattle ranch owners are likely to eat meat because they sell the cattle for money, which in turn can buy them meat to eat.
Fast food - mainly meat, unless you get salads, which cost so much more than a regular hamburger or cheeseburger
State level lawmakers - some would agree with you, but most will not, many think that meat is an important factor in life - food pyramid.

You'd select the Animal rights supporters because meat is made from animals. And the Animals rights supporters sound like they support the rights of animals. A cattle ranch owner wouldn't help you because they are a steakhouse, in which sells cooked animals. Fast food executives sell animal meats as well so they wouldn't be reliable. And State level lawmakers wouldn't help because it mainly focuses on important political decisions. And so the only reliable source left is D, the Animal rights supporters.