The correct answer is (B) Agent; person sent on a mission, or as on a mission, with or without great pomp. A person sent as a messenger or agent. Also, an agent sent on a mission, sometimes in secret, as a spy.

Emissary comes from Latin emissarius (spy) (emiss [from emission] + arius).

Examples of use:

• The President sent an emissary to explore the suitability of a formal visit.
• Each government sent an emissary to the conference on global warming.