The life cycle that becomes more dominant as plants become more complex

The correct answer is sporophyte.

The plants, the gametophyte is the haploid and the sporophyte is the diploid. In the life cycle plants gametophyte is alternates with sporophyte. In complex plants, sporophytes have evolved to become larger, dominant and longer-lived compared to gametophytes. This phase undergoes meiosis and produce spores. Spores germinate to form gametophyte.