What cells are involved in fertilization
a.
diploid
c.
triploid
b.
haploid
d.
all of the above

d.all of the above are involved in the fertilization process.

Explanation:

During the fertilization process, haploid gametes fused to form a diploid cell called zygote. A diploid cell is a cell that contains two sets of chromosome.Gametes are haploid cells. During  sexual reproduction gametes ( sperm & egg) fuse  at fertilization to form a diploid zygote. The zygote develops into diploid organism. The two sperms simultaneously enters the egg to form embryo of triploid cells.The nucleus of the other sperm cells fuses with the two haploid polar nuclei in the centre of gametophyte. The resulting cell is triploid. This cell divides through mitosis and forms the endosperm a nutrient rich tissue inside the seed.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.