After pollen grows a tube down the style, . A: egg cells unite with an embryo
B: chromosomes slpit in half
C: the pollen sticks to the stigma
D: sperm cells travel to the ovary

After pollen grows a tube down the style, sperm cells travel to the ovary (option D).

Explanation:

In angiosperms, the pollen grain contains the male gametophytes that are transported to a flower for pollination to occur.

Once the pollen reaches the stigma of a flower, from it grows a tubal extension, called a pollen tube, which grows into the ovary. The pollen tube allows male gametophytes (sperm cells) to come into contact with female gametophytes (eggs) to fertilize them.

The other options are not correct because:

    A. Egg cells do not attach to the embryo, but to the sperm to produce that embryo.

    B. Chromosomes split in half occurs in cell division.

    C. Pollen sticks to stigma is a process that occurs before the pollen tube is formed.