6. During self-pollination in seed plants, pollen grains (1 point)
swim to female reproductive structures through water.
must be carried from a male cone or flower to a female cone or flower.
carry zygotes to the female structures, which form the seeds.
are carried to female reproductive structures by wind or animals.

During self-pollination in seed plants, pollen grains must be carried from a male cone or flower to a female cone or flower.

Explanation:

Self-pollination refers to a plant's ability to fertilize itself by transferring its pollen from the male to the female sexual organ within the same plant. This mechanism implies the absence of pollinating agents  like water, wind or birds.

The pollen grain represents the male gametophyte, present in the stamen, a male sexual organ. When transferred to the stigma - female sexual organ - the pollen grain hatches, it forms the pollen tube to join the oosphere, the female gametophyte.

Learn more:

Self-pollination link