The correct answer is C) a group formed for a common purpose.
A coalition is a group formed for a common purpose.
A coalition can be understood as a temporary alliance between groups of the same interest. They could be groups with the same political interest, economic interest, and social or cultural interest. These groups from coalitions in order to strengthen their powers or faculties to do something in their favor. It could be a political coalition to support a legislative issue or an economic collition of some industry to support a free trade agreement with other nation.