Ablastocyst is a a blastocyst is a

cluster of cells surrounding a developing egg in the uterus.
membrane that surrounds and protects a growing embryo in the uterus.
growth that can form in the wall of the fallopian tubes.
hollow ball of cells formed after a fertilized cell undergoes cell division.

hollow ball of cells formed after a fertilized cell undergoes cell division

Explanation:

Blastocyte is the name given to a hollow structure, originating from cell divisions that occur after fertilization. It is an embryo 5 or 6 days old (in some cases 7 days) and composed of approximately 200 cells.

Compared to embryos with fewer days, this embryo has a more differentiated cellular structure, composed of a central cavity (blastocele cavity) and two cell types: the trophoectoderm cells (which later will develop and form the placenta) and the cells of the internal mass (which will form the fetus).

The blastocyst represents the stage of embryonic development prior to implantation in the womb.