I am pretty for sure the answer is roots.
Answer:
a. a set of proteins involved in innate but not acquired immunity.
Explanation:
The complement system are a set of proteins or protein fragments that play a major role in the innate immune system. The complement system is involved in the defense of the body from foreign pathogen through specific plasma proteins that participate in leukocyte activation, chemotaxis and opsonization. In other words, they increase the ability of phagocytes and antibodies to mop up damaged cells and foreign microorganism, activate inflammation process.
Some of these proteins include complement component 3 (C3), complement component 9 (C9) and C1Q complex.
The right answer is A: intercellular communication.
An example of intercellular communication is the one between the kidney, liver and lungs to preserve water-soluble homeostasis.
Angiotensinogen, an inactive protein produced by the liver, circulates in the blood. It is the precursor of the active peptides angiotensin I and II, and the only substrate of renin.
In the event of a drop in the pressure in the renal artery, renin (an enzyme sometimes considered as a hormone) is secreted in the kidney by differentiated myoepithelial cells of the arteriole afferent of the juxtaglomerular apparatus. There are also other stimuli promoting renin secretion: decreased natremia in the distal convoluted tubule, ß-agonists, hyperkalemia, PGI2 and stimulation of juxta-glomerular cells by the sympathetic nervous system)
The angiotensinogen is cleaved by the renin and forms a decapeptide called "angiotensin I", inactive.
Angiotensin I will then be converted primarily to angiotensin II by a carboxypeptidase, the angiotensin converting enzyme. This enzyme, secreted by the liver, acts at the pulmonary level.