Which of the following sources might contain research that would support the assertion?

"the uniform jerseys will serve as inexpensive advertising."

an interview with a sponsor from last year
a brochure from the uniform shop that explains pricing
a newspaper article
a brochure from a local advertising shop, showing prices for other similar advertising projects
all of the above

The answer to the question above is the last option: ALL OF THE ABOVE. I can say that everything that is listed above can be considered as credible sources for a research that supports the assertion that the uniform jerseys will serve as inexpensive advertising. Firstly, an interview with a sponsor from last year. This can be considered as a primary source since it is the sponsor that knows how much they have allotted in advertising in uniform jerseys. Secondly, a brochure from the uniform shop with prices. This is also considered a primary source in terms of the prices in making the uniforms. And lastly, a brochure from a local advertising shop with the prices. Since these uniforms have sponsors, depending on the sponsor, the amount will also vary and the pricing is negotiated between the sponsors and the advertising shop.