Why are third parties important in a political system?

They are also termed the succeeding parties.

Explanation:

The united state has numerous third party system and these are since the mid 20th century. In Canada also there exists a third party system and thus are used in most of the countries as they are first past the post voting system, and is rather stronger than the two-party system. Thus in these countries, they are represented to elected to legislatures and have a serious chance of forming the government, as they bring people to the polls.  Are often shared by a network of bond and they are usually included as a network of the political systems.

The answer is d., a mountain.