单项选择题

27.When a stroke occurs,the arteries leading to and within the brain. 　　28.A person’s vision is likely to be affected if a stroke. 　　29.Some people can reduce their risk of stroke if they. 　　30.New treatments are now available to people who. 　　A　suffer from a stroke 　　B　will be affected 　　C　change their lifestyles 　　D　will take place 　　E　occurs at the back of his/her brain 　　F　controls various body functions