Are independent and not associated with the marketing efforts of any particular company or brand.
a. noncorporate blogs
b. e-commerce sites
c. social networking sites
d. e-mail services

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.