What was the Columbian Exchange? What types of disease found their way to the New World to the Old World? (3-4 sentences)

Why was the u.s. annexation of hawaii delayed until william mckinley became president? a: the rebels who overthrew queen liliuokalani opposed u.s. annexation. b: the senate did not approve the treaty of annexation until mckinley entered the white house. c: supporters of the nationalist cause were in the majority in hawaii until 1898. d: mckinley’s predecessor, grover cleveland, refused to sign the treaty of annexation.