A Study Examined the Effectiveness of Botox Injections in the Corrugator

A study examined the effectiveness of Botox injections in the corrugator supercilii muscles for the treatment of chronic migraines. Of the 29 migraine-prone patients participating in the study, 24 reported some form of improvement. Why can we not conclude from the findings that Botox injections in the corrugator supercilii muscles are the cause for these improvements?

A) There is no comparison group, and the improvements could simply be due to the placebo effect.
B) We computed only a confidence interval, not a P-value.
C) We are only 95% confident that our interval captures the true population parameter.
D) The sample size is too small.