The British Party System Is Often Called a "Two-And-A-Half Party

The British party system is often called a "two-and-a-half party system" because the

A) Labour Party has two unofficial wings that operate with different policy objectives.
B) House of Lords is part of government but is not popularly elected.
C) Scottish National Party holds only a regional sway instead of a national one.
D) Liberal Democratic Party trails far behind the Conservative and Labour parties in electoral strength.