Answer the following question given this paragraph: Vascular disorders involve problems with blood flow. For example, a stroke occurs when a blood clot blocks blood flow to part of the brain. Brain cells die quickly if their oxygen supply is cut off. This may cause paralysis and loss of other normal functions, depending on the part of the brain that is damaged. Q: Vascular disorders involve problems with the flow of what? A:
Available choices:
(I) mucus;
(II) bacteria;
(III) saliva;
(IV) blood;
(IV)