(A). Metaphorically, means something which precedes the real business in hand. The reference is to the preliminary canter of horses before the race itself begins.
“The real business of the sessions commenced last night ... Everything that has preceded the introduction of this measure has been a preliminary canter.” —Newspaper paragraph, April 14th, 1894.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894