To solve this problem, we need to analyze the effects of using an artificial kidney during hemodialysis. Let's evaluate each statement:$\newline \bullet$Nitrogenous waste build-up in the body:$\newline$ - Hemodialysis is specifically designed to remove nitrogenous wastes from the blood.$\newline$ - Therefore, this statement is incorrect.$\newline \bullet$Non-elimination of excess potassium ions:$\newline$ - Hemodialysis effectively removes excess potassium ions from the blood.$\newline$ - Therefore, this statement is incorrect.$\newline \bullet$Reduced absorption of calcium ions from the gastrointestinal tract:$\newline$ - Hemodialysis does not directly affect calcium absorption from the gastrointestinal tract.$\newline$ - However, patients on dialysis often have altered calcium and phosphate metabolism, which can indirectly affect calcium absorption.$\newline$ - Therefore, this statement can be considered correct.$\newline \bullet$Reduced RBC production:$\newline$ - Hemodialysis patients often experience anemia due to reduced erythropoietin production by the kidneys.$\newline$ - Erythropoietin is a hormone that stimulates RBC production.$\newline$ - Therefore, this statement is correct.$\newline$Based on the analysis, the correct statements are:$\newline$Reduced absorption of calcium ions from the gastrointestinal tract and Reduced RBC production.$\newline$This corresponds to Option 3: (c) and (d) are correct.