Which of the Following Descriptions Characterizes a Problem with the Use

Which of the following descriptions characterizes a problem with the use of case descriptions as an evaluation method?

A) They lack statistical documentation,despite telling about an interesting event.
B) They have to be repeated in order to verify that no other factor could have changed the outcomes.
C) They are not considered "good" research.
D) They cannot prove that the nursing intervention led to the specific health outcomes.