VANGUARD :

Race driver
Officer
Flag bearer
Pioneer

The correct answer is D. Pioneer.

A vanguard is a person or group that leads the way in a new or difficult undertaking. The word comes from the Old French word avant-garde, which means “advance guard.” A vanguard can be a military unit that leads an attack, or it can be a group of people who are at the forefront of a social or political movement.

A race driver is a person who drives a car in a race. An officer is a person who holds a position of authority in the military, government, or another organization. A flag bearer is a person who carries a flag during a parade or other event.

All of these words have something to do with being ahead of others, but only a pioneer is someone who leads the way in a new or difficult undertaking.