Which of the Following Helps Explain Why Union Density Falls

Which of the following helps explain why union density falls far short of union coverage in most of Europe?

A) Affiliation to unions is regarded with suspicion by most employers which,in turn,negatively affects employee prospects.
B) Mandatory membership is not important.
C) Exclusive representation is a requirement in most countries.
D) Higher job satisfaction among workers dilutes the role of unions.