We just finished this unit, and The answer is A.
I can certainly see how this is likely to be a science book. With the latest photographic technology scientists have photographed everything from star nebulas, space gases, to exoskeletons of creatures, flowers, sun flares, waves in motion, inside cells, etc. so yes absolutely!
The primary role of hydrochloric acid is to sterilize the food you eat and to prevent harmful bacteria from entering the GI tract. HCL also triggers the release of enzymes such as pepsin which are essential for the digestion of protein.
I believe the answer is adaptation
<span>Protein is made up of building blocks called amino acids</span>
