In order for a physical barrier to be effective in preventing infection, the barrier must a. prevent the substance from entering the body, trap the substance when it first enters the body, or flush the substance out of the body b. destroy the substance before it enters the body, prevent the substance from reproducing, or flush the substance out of the body c. trap the substance in the body, remove the substance from the body, or prevent the substance from reproducing d. flush the substance from the body, transport the substance in the body, or destroy the substance in the body