A study is being done on a group of people to decide the harm of fast food to the body. The patients have their own choice on whether or not they choose to eat the food and the doctors just observe the results. What type of sample or survey is this? A. observational study B. self-selected C. controlled experiment​

The swimming pool is open when the high temperature is higher than 20∘c. lainey tried to swim on monday and thursday (which was 3 days later). the pool was open on monday, but it was closed on thursday. the high temperature was 30∘c on monday, but decreased at a constant rate in the next 3 days. write an inequality to determine the rate of temperature decrease in degrees celsius per day, d, from monday to thursday.