Questions: Most digestion and absorption occur in the: A. jejunum and ilium. B. ileum and cecum. C. ilium and colon D. duodenum and first third of the jejunum.

The answer is D: duodenum and first third of the jejunum.

Explanation for each option:

A. Jejunum and ilium: This option is incorrect because "ilium" is a misspelling of "ileum." While the jejunum is indeed a major site for digestion and absorption, the ileum primarily absorbs vitamin B12, bile salts, and any remaining nutrients.

B. Ileum and cecum: This option is incorrect because the ileum, while involved in absorption, is not the primary site for most digestion and absorption. The cecum is part of the large intestine and is mainly involved in absorbing fluids and salts that remain after intestinal digestion and absorption.

C. Ilium and colon: This option is incorrect because "ilium" is a misspelling of "ileum," and the colon is primarily involved in absorbing water and electrolytes, not in digestion and absorption of nutrients.

D. Duodenum and first third of the jejunum: This option is correct because the duodenum is the first part of the small intestine where most chemical digestion occurs, and the first third of the jejunum is where a significant amount of nutrient absorption takes place.

In summary, most digestion and absorption occur in the duodenum and the first third of the jejunum.