Pilot
Forerunner
Steward
Messenger
Answer is Wrong!
Answer is Right!
The correct answer is B. Forerunner.
A forerunner is someone or something that comes before another and indicates or prepares the way for its coming. In other words, a forerunner is a harbinger.
A pilot is someone who operates an aircraft. A steward is someone who manages the domestic affairs of a household or institution. A messenger is someone who carries messages.
While all of these words have some similarities to harbinger, only forerunner is a perfect synonym.