Question

_____ are independent and not associated with the marketing efforts of any particular company or brand.​

Answer 1

A. Noncorporate blogs are independent and not associated with the marketing efforts of any particular company or brand.​ 
The other options are tied to a particular company or brand and are often advertised so as to attract a larger audience of people who will start using them. Noncorporate blogs do not do that - they do advertise, but are not linked to any company whatsoever.