In any experiment, it is important to collect, observe and study the input of other scientists, the application of advanced technologies (when it's available), the knowledge of the process in progress and also the inferences from data. But the study of other scientists and the knowledge of the process (in this case, photosynthesis) must be observed since the beginning, while planning the experiment and building arguments to defend the importance of the study. The advanced technologies is applied as as part of the methodology of the study, being important as a means of getting results. What is really connected to the conclusions, the main thing in which the results are based on, is the data collected from the study. This is what provides new insights and discoveries that will be intepreted using the information from other scientists and previous knowledge, but only the process of the experiment can give us the data that will support the conclusions. Therefore, the correct answer is (3) careful observation, measurements, and inferences from his data.