N 2010, three top b2b were thermo scientific lab and research supplies ($10.8 billion); henry schien dental, medical, and vet supplies ($7.5 billion); and wesco international electrical and industry maintenance supplies ($5.0 billion).

The answer to the blank space is Catalog sellers.
B2B refers to a situation where one business makes a commercial transaction with another. For many, selling on B2B market places is a great way to expand businesses and sell more products to more customer. The most important thing in B2B is to understand how service companies differ from their product-selling counterparts. B2B companies that sell products tend to be very sales focused, they wait to sell as many products as they can. 

Nitrate poisoning for the first onebaby blue syndrome

D.) domain, kingdom, phylum, class, order, family, genus, species