Explanation:

There are different types of PR systems that exist in different countries. The variations in the PR system depend on the electoral system, the number of political parties, the size of the electorate, and the political culture of the country.

Types of PR Systems:

1. Closed list proportional representation: In this system, voters choose from a list of candidates presented by political parties. The parties rank the candidates in the list, and the seats are allocated based on the percentage of votes received by each party.

2. Open list proportional representation: In this system, voters have the option to vote for individual candidates rather than a party list. The seats are allocated based on the percentage of votes received by each candidate.

3. Single transferable vote: In this system, voters rank candidates in order of preference. Candidates who receive a certain quota of votes are elected, and any surplus votes are transferred to the voters' second-preference candidates.

4. Mixed member proportional representation: In this system, voters cast two votes, one for a candidate in a single-member constituency and another for a political party. Seats are allocated based on the percentage of votes received by each party.

Number of Variations:

There are two main types of PR systems - Closed list PR and Open list PR. However, there are variations within these two types of PR systems, such as:

- The number of seats allocated to each constituency
- The threshold percentage of votes a party needs to win a seat
- Whether voters can choose their preferred candidate or only vote for a party list

Therefore, there could be several variations in the PR system depending on the specific rules and regulations of each country. However, the answer to the question is option B, which is two, as there are two main types of PR systems - Closed list proportional representation and Open list proportional representation.