The small intestine uses segmentation to mix chyme with digestive enzymes, increase its contact with the mucosa, and propel it forward through the digestive tract.

A. Esophageal glands secrete mucus to lubricate the esophagus, but they do not cause acid reflux.

B. Pharyngeal constrictors are muscles that help in the swallowing process, not in preventing acid reflux.

C. The lower esophageal sphincter (LES) is a ring of muscle that controls the passage of food from the esophagus to the stomach. If the LES is weakened or relaxes inappropriately, stomach acid can flow back into the esophagus, causing acid reflux or "heartburn."

D. The upper esophageal sphincter controls the passage of food from the pharynx into the esophagus, but it is not involved in preventing acid reflux.

A. Corpus luteum; FSH and LH: The follicle transforms into the corpus luteum after ovulation, which secretes hormones. However, FSH and LH are hormones secreted by the pituitary gland, not products of the corpus luteum.

B. Corpus albicans; progesterone: The corpus albicans is a degenerated form of the corpus luteum and is not responsible for secreting progesterone.

C. Corpus albicans; estrogen and progesterone: The corpus albicans forms after the corpus luteum degenerates and does not produce significant levels of estrogen and progesterone.

D. Corpus luteum; estrogen and progesterone: After ovulation, the follicle transforms into the corpus luteum, which secretes estrogen and progesterone to support the early stages of pregnancy or regulate the menstrual cycle if pregnancy does not occur.