Final answer:
Thrombotic strokes are the most common type of stroke with a gradual onset, caused by the blockage of blood flow to the brain due to a blood clot forming within an artery.
Step-by-step explanation:
Of the four types of strokes mentioned, thrombotic strokes are the most common and typically have a gradual onset. Thrombotic strokes occur when a blood clot forms in one of the arteries supplying blood to the brain, leading to ischemia — the loss of blood flow to brain tissue. This blockage most often results from atherosclerotic plaques lining the vessel walls and can lead to a buildup that obstructs blood circulation. Unlike hemorrhagic strokes, which involve bleeding in the brain and can have a more sudden onset, thrombotic strokes can develop over time as plaques grow, making their onset more insidious and often gradual. Lacunar and embolic strokes are also types of ischemic strokes but are not specifically characterized by a gradual onset like thrombotic strokes are.