Heartburn is usually caused by the .a. irritation of the lower esophagus by substances in spicy food. b. reflux of chyme from the stomach into the lower esophagus. c. secretion of acid by the lining of the lower esophagus. d. retention of food at the bottom of the esophagus by a sphincter that is reluctant to open.

b. reflux of chyme from the stomach into the lower esophagus.

Explanation:

Heart burn occurs when reflux of chyme (an acidic fluid containing partially digested and gastric juices formed in the intestine and stomach during digestion) moves from the stomach into the lower esophagus. In other words, when stomach acid flow into the lower esophagus (acid reflux), it results to heart burn.

Heart burn can lead to a serious medical condition if not treated on time, like, Gastroesophageal Reflux Disease (GERD). In few cases, it could lead to esophageal cancer.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.