Answer: Option A
:
A
When the sperm fertilises the egg, the single-celled fertilised egg is called the zygote. The zygote undergoes repeated cell divisions to form a stage called the blastocyst. In this stage, there is a sphere of cells which encloses a inner mass of cells. The inner mass of cells develops into anembryo. As the embryo develops, from around the 11th week it is known as a foetus.