Vitamin D is not really a vitamin, but a precursor for the most potent steroid hormone in the human body. It can be obtained from exposure to the sun’s ultraviolet (UV) radiation, especially during the early morning hours.

Correct Option: D

Vitamin D is not really a vitamin, but a precursor for the most potent steroid hormone in the human body. It can be obtained from exposure to the sun’s ultraviolet (UV) radiation, especially during the early morning hours.

Plants reduce the CO₂, because they use it with photosynthesis. They use it to give oxygen and carbohydrates as the final product. It is for this reason that plantation of trees has been stressed by environmentalists.

Correct Option: B

Plants reduce the CO₂, because they use it with photosynthesis. They use it to give oxygen and carbohydrates as the final product. It is for this reason that plantation of trees has been stressed by environmentalists.

Human immunodeficiency virus infection / acquired immunodeficiency syndrome (HIV/AIDS) is a disease of the human immune system caused by the human immunodeficiency virus (HIV).

Correct Option: B

Human immunodeficiency virus infection / acquired immunodeficiency syndrome (HIV/AIDS) is a disease of the human immune system caused by the human immunodeficiency virus (HIV).

Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine tri-phosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in other tasks such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth.

Correct Option: D

Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine tri-phosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in other tasks such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth.

Nephron is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. A nephron eliminates wastes from the body, regulates blood volume and blood pressure, controls levels of electrolytes and metabolites, and regulates blood pH.

Correct Option: C

Nephron is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. A nephron eliminates wastes from the body, regulates blood volume and blood pressure, controls levels of electrolytes and metabolites, and regulates blood pH.