Many things can be made in the field and laboratory, but I think that the safest answer is "observation" - observation is what is usually done in the field, where one does not have the possibility for experiments, or only rarely so. In the lab, one usually performs experiments, but observations are also common, so observation is what connects the two.
The 3 authors purposes are persuade, inform and entertain. Persuade the author is using their opinion to try and get you to agree, inform the author is explaining a topic with facts and without bias, and entertain the work doesnt have either of those it will be amusing or fun
