Which body system is directly attacked by HIV?

HIV is a virus that weakens and destroys the body's immune system. It attacks and destroys the immune cells, specifically CD4 cells, in the body which are responsible for fighting off infections and diseases. Therefore, the correct answer is C, the immune system. Option A, the respiratory system, is not directly attacked by HIV. It is possible for someone with HIV to develop respiratory infections due to their weakened immune system, but it is not the direct target of the virus. Similarly, option B, the cardiovascular system, is not directly attacked by HIV. While chronic inflammation caused by HIV can increase the risk of cardiovascular disease, the virus itself does not directly attack the heart or blood vessels. Option D, the nervous system, is also not the direct target of HIV. While there is a risk of developing neurological complications due to HIV, such as dementia or peripheral neuropathy, the virus does not directly attack the nervous system.