All of the following people were members of the "united opposition" except:
a. trotsky.
c. kamenev.
b. stalin.
d. zinoviev.

The only mentioned character that was not part of the United Opposition was:

b. stalin.

Explanation:

The United Opposition was an organized party that was born to fight for more freedom and inside the communist party and less bureaucracy. Their founders were Leon Trotsky, Grigory Zinoviev, and Lev Kamenev. They opposed to Joseph Stalin's control and closed ideas that limited the progress of the party and country.

well stockyards mean a large yard containing pens and sheds, typically adjacent to a slaughterhouse, in which livestock is kept and sorted. and i'm assuming that by party you   mean a large group of people which does make sense because chicago is a very crowded place much like new york. stockyards tend to take up a lot of room due to needing the area for pens to keep animals in and the fact that stockyards are usually right by slaughterhouse where they process and distribute the product. so its much like a zoo but with some dead animal products close by.