Complex sentence: Between 1955 and 1974 the DLP was able to command a significant vote, particularly in Victoria and Queensland, and during the period held between one and five seats in the Senate (which is elected by proportional representation).
Split into simpler sentences: Between 1955 and 1974 the DLP was able to command a significant vote, particularly in Victoria and Queensland. During the period the DLP held between one and five seats in the Senate (which is elected by proportional representation).