A study is done to determine which steroid cream is more effective for bug bites. If the only bug bites treated in this study were mosquito bites, which of the following is true?
a) The study will only be able to produce results concerning the effect of the steroid creams on mosquito bites.

b) The steroid cream that is found to be the best will only work for mosquito bites.

c) The observational study is inherently biased.

d) The steroid cream that is found to be the best will work for all bug bites.