What Is the Principal Disadvantage of the Descriptive and Correlational

What is the principal disadvantage of the descriptive and correlational research methods

A)  Because of practical or ethical reasons, they cannot be used to study some research questions. 
B)  They do not allow the researcher to describe behaviour. 
C)  They frequently observe behaviour in artificial situations. 
D)  Because researchers cannot control variables of interest, conclusions concerning cause-and-effect relationships are not appropriate.