<span>blastocyst
The outer layers of the blastocyst turn in to the trophoblast after implantation. The trophoblast forms the placenta.</span>
<span>Primary immunodeficiencyvdiseases are a group of more than 250 rare, chronic disorders that affect how the body’s immune system works. Primary immunodeficiency diseases are caused by genetic defects. I hope this helped</span>
the answer is chemical reaction
