My feet are swollen, what could be the cause of the swelling?

Many things. Tehre are numerous things that can make your feet swell. I would suggest elevating the feet as often as possible and watch your salt intake. If the swelling persists i would check with your doctor to find out why you are swelling and then find a more accurate treatment.
Several things. It could be due to extreme heat. It could be due to improperly working valves in the veins of your legs especially if you have vericose veins. It could be from kidney or heart problems. If it persists i would see your doctor.