Why Is the Motivation to Join Labor Unions Lesser in Europe

Why is the motivation to join labor unions lesser in Europe than in the United States?

A) Because negotiated agreements in major industries are usually adopted by other employers.
B) Because a high level of involvement in complex contract negotiations is mandated at the plant level.
C) Because unlike in the United States,labor unions in Europe are mostly organized along religious lines and are therefore very rigid.
D) Because affiliation to labor unions is considered politically subversive in Europe and is discouraged by the government.