The correct option is C endometrium
Uterine milk is a white secretion from the endometrium. It contains proteins and amino acids which will nourish the embryo during development. Mitotic divisions within the zygote termed cleavage results in 8-16 blastomeres cells stage called a morula. Morula continues to divide and transforms into blastocyst as it moves further into the uterus in four days. It is still surrounded by the zona pellucida and is of the same size as the original zygote. The rapid cell division by mitosis division consequently decreases the cytoplasmic to the nuclear volume. Morula floats in the uterine lumen for three days. The glycogen rich secretion from the glands of the endometrium called uterine milk enters the floating morula for nourishment through zona pellucida.
The wall of the uterus or womb has three layers, as follows: the outermost perimetrium and the innermost endometrium which lines the uterine cavity. The sandwiched layer between the endometrium and perimetrium is the myometrium made of smooth muscles which help in the contraction of the uterus in labor.
The zona pellucida is a thick extracellular coat of the ovum. It induces changes in the membrane that restricts polyspermy (fertilization of the egg by multiple sperms) of the ovum. Sperm enters the ovum through the zona pellucida and the plasma membrane.