Because their economy was based on mercantilism, why were the colonies so important to Britain? A) The colonists provided raw materials and markets for finished goods.
B) The colonists provided necessary tax revenue.
C) The colonists sent soldiers to serve in the British army.
D) The colonists protected the land from being taken over by France,

I would personally say "A) The colonists provided raw materials and markets for finished goods."

Explanation:

Mercantilism itself is believing in profitable trading/commercialism. The Colonies produced vast amounts of Raw Materials and valuables like Grain, Sugar, and Tobacco. The British Parliament also passed many The Navigation Acts over the years, basically preventing the Colonies from Trading with anyone other than Great Britain.

use wikipedia, i think they have this.