The answer should be the letter D
It gets blurry and further away because it is not changing
The white blood cell identifies the toxin produced by the pathogen and creates antibodies to fight the pathogen
Since the other answer got deleted, i'll just answer it for you.
a sinoatrial node is the main pacemaker that begins each heartbeat located in the junctions of superior vena cava and the right atrium. It signals from the node that spread through the atria and determines the heart rates.
