Many individuals do not show physical changes of aging until their seventies and even eighties?

Answer:

D

Explanation:

Gastric acid, gastric juice, or stomach acid, is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid plays a key role in digestion of proteins by activating digestive enzymes, which together break down the long chains of amino acids of proteins. Gastric acid is regulated in feedback systems to increase production when needed, such as after a meal. Other cells in the stomach produce bicarbonate, a base, to buffer the fluid, ensuring a regulated pH. These cells also produce mucus – a viscous barrier to prevent gastric acid from damaging the stomach. The pancreas further produces large amounts of bicarbonate and secretes bicarbonate through the pancreatic duct to the duodenum to neutralize gastric acid passing into the digestive tract.

The active components of gastric acid are protons and chloride. Often simplistically described as hydrochloric acid, these species are produced by parietal cells in the gastric glands in the stomach. The secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the "hydrochloric acid" is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, a level maintained by the proton pump H+/K+ ATPase.[1] The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide.

The highly acidic environment in the stomach lumen degrades proteins, e.g. food. Peptide bonds, which comprise proteins, are labilized. The gastric chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen, and in infancy rennin). The low pH activates pepsinogen into the enzyme pepsin, which then aids digestion by breaking the amino acid bonds, a process called proteolysis. In addition, many microorganisms are inhibited or destroyed in an acidic environment, preventing infection or sickness.

Answer:      i think that its D and that might be just my opinion

Explanation:

                all of the are good answers but if you get it wrong i truly apologize

It is a person's choices and preferences outside of work that define personal life, including one's choice of hobbies, cultural interests, manner of dress, mate, friends, and so on. In particular, what activities one engages in during leisure-time defines a person's personal life.

Apart from hunter-gatherers, most pre-modern peoples' time was limited by the need to meet necessities such as food and shelter through subsistence farming; leisure time was scarce. People identified with their social role in their community and engaged in activities based on necessity rather than on personal choice. The modern conception of "personal life" is an offshoot of modern Western society. Modern people tend to distinguish their work activities from their personal life and may seek work–life balance. It is a person's choices and preferences outside of work that define personal life, including one's choice of hobbies, cultural interests, manner of dress, mate, friends, and so on. In particular, what activities one engages in during leisure-time defines a person's personal life.