The correct answer is option 3. The presence of air bubbles in the bloodstream can be dangerous to life because it obstructs the flow of blood. When air bubbles enter the bloodstream, they can block or clog blood vessels, preventing blood from reaching vital organs and tissues. This can lead to tissue damage and organ failure. It is important for blood vessels to remain clear and unobstructed to ensure efficient delivery of oxygen and nutrients to the body`s cells. Option 1, air combining with blood forming a complex, is not a correct explanation as air does not form a complex with blood. Option 2, the flow of blood increases manifold, is incorrect as the presence of air bubbles does not necessarily affect the flow of blood. Option 4, the pressure of blood increases manifold, is also incorrect as air bubbles do not directly cause an increase in blood pressure.