Which method would be the BEST way to conduct an observational study to determine the effects of vitamin C for preventing colds? Ask 100 people who consume vitamin C if they got a cold. Divide 100 volunteers into two groups; one group will consume vitamin C and the other group will not consume vitamin C. After a period of time, see how many people in each group developed a cold. Interview 100 people and classify them as either never consuming vitamin C, sometimes consuming vitamin C, or consuming vitamin C on a regular basis. Check for any cold symptoms in all the patients and analyze results. Ask 100 people who had a cold last winter if they consumed vitamin C on a regular basis and record the number