Which of the following describes a thrombus?

• A. A clot travels through the bloodstream.
• B. A clot that forms in a vessel.
• C. A nerve impulse.
• D. An infection.

Answer: (B)

A thrombus is a blood clot that forms in a vessel and stays there, potentially blocking blood flow. It develops at the site of vessel injury or along a area of slow blood flow and involves components like platelets and fibrin. This is different from a clot that travels through the bloodstream, which is called an embolus. The other options don’t describe a stationary clot in a vessel—nerve impulses are electrical signals in nerves, and infection refers to invading microorganisms or the inflammatory response.