Pahami pentingnya sistem kekebalan tubuh yang kuat. Lakukan olahraga secara teratur. Makanlah sayuran berdaun hijau. Minum suplemen vitamin C. Tidurlah yang cukup setiap malam. Berhentilah merokok dan hindari penyebab iritasi berbahaya lainnya.

Given the above summary, write a detailed text in English for it.
When your immune system is functioning properly, it can help to fight off many infections that can lead to a URI; however, keeping your immune system strong can take a little bit of work, but there are many things you can do that can boost your immune system's strength. When you exercise regularly, you can keep the neutrophil function in your white blood cells running properly. This function is partly responsible for fighting off infection. Moderate exercise includes brisk walking, jogging, biking, or swimming. Try to exercise for 30 minutes five times a week when possible. These vegetables, which are also called cruciferous vegetables, can help to make your immune system stronger by regulating intra-epithelial lymphocytes in your body. These lymphocytes are stimulated by aryl hydrocarbon receptors (AhRs), which are responsible for the first line of defense in your body against foreign substances that enter your body. They also help with wound repair. Try to eat four to five servings of green leafy vegetables every day. This vitamin is an antioxidant that may help to strengthen your immune system. Vitamin C can help to kill free radicals in your body, which can lead to infections if allowed to develop unchecked. You can take a vitamin C supplement each day; aim to get roughly 500 mg to 1,000 mg of the antioxidant per day. You can also eat foods rich in vitamin C. These foods include citrus fruits like oranges, lemons, kiwis, mangoes, cantaloupe, papaya, pineapple, berries and watermelon. When you do not get enough sleep, it reduces your immune system's ability to function as well as the functions of many other systems in your body. When you sleep, your body grows and repairs damaged cells and tissues, making your body stronger when it comes to fighting infection. Everyone needs a different amount of sleep, depending on your age, lifestyle, and a variety of other factors; however, in general, adults who are 18 years and older need roughly seven to nine hours of sleep, while school-aged children need between...