This question describes a condition called atrophic gastritis where inflammation of the wall of the stomach, causes the natural healthy tissue to die and become replaced by non-functional scar tissue.
There are many different cells in the wall of the stomach with different functions. When atrophy occurs you lose these cells and the benefits they provide your body.
Some cells in the wall of your stomach produce "intrinsic factor" which is a protein that binds vitamin B12 and allows your intestines to absorb the vitamin. This vitamin plays an important role in DNA synthesis, and a deficiency most commonly manifests as anemia, or low red blood cell count. In this setting, the anemia is called pernicious anemia.
Therefore, the correct answer is 1.
The answer is not 2 because duodenal ulcers form when there is too much acid production in the stomach or a loss of protection in the duodenum.
The answer is not 3 because when you lose the cells in the wall of your stomach, you also lose the cells that produce acid.
The answer is not 4 because gastrin is a hormone that is mainly produced in the small intestine to tell the stomach to produce more acid. The small intestine is not damaged in this disorder so gastrin levels do not change.