In the workplace, the "open shop" meant
a) skilled workers were required to join a craft union.
b) workers had no right to join a union.
c) workers would be allowed to come and go as they .
d) no worker was required to join a union.
e) labor unions had the right to organize that particular industry.

D. No worker was required to join a union.

Explanation:

Open shop implies a manufacturing plant, office, or different business foundation in which an union, picked by a larger part of the workers, goes about as illustrative of the considerable number of representatives in settling on concurrences with the business, yet in which union membership is not a state of being contracted.

in terms of experimental research, mcdonald’s charging different prices in the two cities relates to