Answer
Experimental
Step-by-step explanation
An experimental research is any conducted research with a scientific approach where a set of variables are kept constant while the other set of variables are measured as the subject of the experiment.The study involves the random assignment of participant into different groups.
To be considered as an experimental study, it should give some sort of treatments to a group and recording the effects. (such as controlling type of mil children drink). Despite the uncertainty whether the result is accurate.