Insulin is a hormone produced by the pancreas that plays a crucial role in regulating blood sugar levels. The correct answer is option 2, which states that insulin decreases blood sugar. This is because insulin helps cells take in glucose from the bloodstream, thus lowering the concentration of glucose in the blood. When blood sugar levels are high, the pancreas releases insulin to promote the uptake and storage of glucose in cells, such as liver and muscle cells. This process helps to maintain a stable blood sugar level. Therefore, insulin is essential in preventing hyperglycemia, a condition characterized by high blood sugar levels. It is important to note that insulin does not directly affect blood vessels or stimulate lactation.