The Pierce Administration's Secret Scheme to Gain Control of Cuba

The Pierce administration's secret scheme to gain control of Cuba was stopped when

A) Spain threatened a pre-emptive war against the United States.
B) the secret Ostend Manifesto was leaked to the public.
C) U.S.leaders signed the Clayton-Bulwer Treaty.
D) Spain declared that it would abolish slavery in Cuba.
E) U.S.adventurers bungled their invasion.