Answer -
T-Cell - White blood cell = Fight off Intruders in the body
B-Cell - Macrophages = Creates Antibodies against antigen.
Cell Differentiate - Stem Cells = My favorite cell of all time in animal because they can turn into almost any cell like neural, signaling, euthyroid. Etc
I think the correct answer would be A. The yolk sac becomes the placenta. It is membranous sac that is attached to the embryo. It provides all the nutrition and the blood cells needed by the embryo. It is also called the umbilical vesicle.
Most likely synapses because it’s gaps
The population will later, cease to exist.
Since the population is experiencing (about) the same rates of immigration and emigration, these 2 factors will not change anything.
A low birth rate and a high death rate means that more people are dying than being born.
Therefore the population will decrease until there is nobody and it will cease to exist.