A researcher is conducting a study on Parkinson's disease. For the 100 patients he interviews, he records their gender, annual income, occupation and weight. He finds that 50% of the interviewed subjects who have Parkinson's disease work in the service industry, and concluded that working in the service industry causes one's chance of getting Parkinson's disease to increase. Which of the following statements is/are correct about the researcher's claim?

A. The researcher cannot make such a claim since this is an observational study.
B. The researcher cannot make such a claim since 50% is too small.
C. Both (A) and (B).
D. Neither (A) nor (B).