Read the following paragraph and choose the option with the set of words which would fill the blanks correctly in the given order.
During fertilisation, the sperm cell from the father and the egg cell of the mother fuse to form a W which divides repeatedly to give rise to a ball of cells. The cells begin to develop into different organs and tissues. This developing structure called X gets embedded in the wall of Y . The stage of X in which all body parts can be identified is called Z .
W, X, Y, Z respectively are :

The correct answer is zygote, embryo, uterus, foetus.

Let us break down the stages of human reproduction and development mentioned in the paragraph step-by-step:

1. W (Zygote): During fertilisation, the sperm cell (male gamete) fuses with the egg cell (female gamete) to form a single-celled zygote. This zygote then divides repeatedly through mitosis to form a ball of cells.

2. X (Embryo): As the cells continue to divide and differentiate into specialized tissues and organs, the developing structure is called an embryo.

3. Y (Uterus): The embryo moves into the womb and gets attached to or embedded in the thick inner wall of the uterus for further growth. This process is known as implantation.

4. Z (Foetus): As development progresses, the stage of the embryo where all major body parts (such as hands, legs, head, eyes, etc.) become clearly identifiable is termed a foetus.

Therefore, W, X, Y, and Z correspond respectively to: W = zygote, X = embryo, Y = uterus, Z = foetus.