Please help me asap, I will report any links or files in which type of statistical study is the population influenced by researchers?

OA. survey
OB. experiment
OC. observational study
OD. researchers do not influence the population in any of the statistical studies ​

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)

Standard deviation of 19,29,21,22,23

Click an item in the list or group of pictures at the bottom of the problem and, holding the button down, drag it into the correct position in the answer box. release your mouse button when the item is place. if you change your mind, drag the item to the trashcan. click the trashcan to clear all your answers. solve this quadratic equation using the quadratic formula. 2x2 - 2x=1 need asap