Which of the following is NOT likely to be true of a study using opportunistic sampling?
a. Some of the cases might be similar to those used in critical-case, negative-case, and extreme-case sampling.
b. The cases that are studied might alter the focus of the study.
c. The researcher has a firm research plan that is clearly stated before the research starts.
d. The researcher is able to take advantage of opportunities that present themselves during the research process.